I guess you should know that Toronto is a huge city, and you'll never be able to see And experience even a fraction of it in a one-day visit. Which means you should plan a very specific itinerary based on your interests that will allow you to spend the day in one part of the city. When you return (and I'm sure you will once you realize what a great city you have just an hour away), you can do something else, and so on, until you have a better idea of what Toronto has to offer.
You have to realize that Toronto is the size and scope of Chicago. There is the Old City - the downtown, if you will, which was the original Toronto, the most urban part of the city, which contains the city's business district, it's entertainment district, many of its galleries, museums, theatres, opera house, symphony orchestra, ballet company, and its famous theatres for musicals and plays, as well as its oldest and most famous neighbourhoods, which are numerous and extremely diverse in ethnic makeup, character, style, and income level (although Old Toronto is becoming more and more like Manhattan, and its middle-income and low-income neighbourhoods have largely disappeared or are diluted by much wealthier residents.
Beyond the Old City are its "boroughs", which were their own municipalities up until 1998, when our then-premier, in conjunction with the mayor, merged them all together, creating what we now know as Toronto. Toronto's boroughs - Scarborough, North York, Etobicoke, York, and East York are generally less densely populated, and though they have many clusters of high-rise apartment towers, have a more suburban layout, with lots of tightly-spaced bungalows, semis, townhouses, and some detached two-storey homes laid out in cul-de-sacs and winding residential streets separated from the main grid of commercial thoroughfares. Like Old Toronto, the "boroughs" are extremely diverse in character, even more culturally and ethnically diverse, although they lack some of the amenities and "attractions" of Old Toronto, have most of the city's low-income pockets, and are dominated by cars and buses.
Before I give you all kinds of details, I thought I should let you know....Toronto is laid out on a grid system, and is quite easy to navigate. Always keep in mind that the Lake is south of the city, so north is always away from the Lake, and South is towards the lake. Since city streets, and the transit system generally runs north/south, east/west, it's important to know this so you can always orient yourself by figuring out where the Lake is in relation to you. Once you know that, you can easily establish north/south, east/west. Another helpful feature of our east / west thoroughfares is the fact that East and West are added to their name depending on which side of Yonge Street they are on. So Dundas St. West is west of Yonge,
And Dundas St. East is east of Yonge. At major intersections, street signs above traffic lights will indicate West or East, so this can help you orient yourself in relation to Yonge. Once you know we're you are in relation to Yonge St. and the Lake, you will always know which way is east, west, north, and south.
For most visitors, Old Toronto is the place they want to be, as it has most of the city's attractions, and is built as a typical old-school compact urban area, it's streets crowded with pedestrians, cyclists, streetcars and buses, as well as cars. It has a decent subway network, and it is easy to get around by public transit. Since I'm sure you are driving here, I would find a lot (my personal favourite is at Dalhousie and Queen, between Church St. and Jarvis. It's right in the heart of the downtown, steps from Yonge St. and the subway, yet it's not too crowded or too expensive to park for the day. Should be $20 or less. Of course, for all I know, the parking lot has been sold to a developer and is now under construction. The city is currently going through one of the largest building booms in the Western World and things change very fast), ditch the car, and spend your day walking, or taking transit if need be.
I'd really like to know what your interests are so I can steer you in right direction. But if you don't have anything specific in mind, checking out the central part of the downtown might be a good first step. If you park at the lot I mentioned, or any lot in the central part of the city (I'm going to add a note at the bottom of my post with some further info about parking). Areas of interest in the central-most part of the downtown are Yonge St. (A major commercial thoroughfare that is very similar to Times Square in the sense that it was once the seedy home of bawdy houses, peep shows, massage parlours, strip clubs, and porn theatres, but has since become a tourist Mecca with a large square (Yonge and Dundas Square) that is typically packed with tourists, features all kinds of free entertainment, and is now a stretch of various shops, clothing and shoe stores. Dundas Square, Eaton Centre, and Queen St. West (from University Ave., west all the way to Gladstone Ave., Queen Street is doubtless Toronto's hippest street, with all kinds of unique shops, eateries, bistros, bars, cafes, galleries, as well as two bastions of Toronto's hip entertainment scene - the Gladstone and Drake Hotels, which were two transient hotels in an area that was home to many of the city's down and out).
Personally, to get a general idea of the flavour of the city, I would park at a lot downtown, visit Dundas Square, then walk the short distance south to Queen St. Walk west to Spadina, taking note of all the many sights and shops along the way. If you want (and I highly recommend it), you can walk north on Spadina to check out the main commercial thoroughfare of Toronto's Chinatown. Many people (even Torontonians) think that Spadina = Chinatown, but Dundas St. is also packed with Chinese businesses both east and west of Spadina, while the adjacent Baldwin Village (a great neighbourhood you can check out when you have more time) and Kensington Market have a large Chinese presence, with many residents of Chinese descent, community centres, churches, and other important non-commercial fixtures in the Chinese community. But Spadina Ave. just north of Queen St. is the busiest, densest commercial area in Chinatown, and worth a look. Make sure to explore the little shops and also the many alley and lane ways, which are very safe and will often lead you to some unique surprises.
Although Toronto has some of the best Chinese food outside of China, ironically you will be hard-pressed to find any of it in Chinatown. Most of the restaurants serve mediocre food, and aren't worth visiting. However, there are a couple aces that specialize in Chinese BBQ, and noodle dishes with fresh noodles made at the front of the restaurant, in view of its patrons. My favourite is a little spot called Gold Stone. It's on the West side of Spadina, just below Dundas, and has large glass panels as its facade, so you can see clearly into the restaurant. It also has a large BBQ counter at the front of the restaurant. Stick with the noodle dishes. My favourite are the noodle soup with Their excellent BBQ items. Noodle Soup with BBQ Pork and Duck is my favourite, and along with an order of fried dough and a Coke, you have a delicious $6.00 meal.
Anyways, enjoy your walk around Chinatown, but you should definitely check out Kensington Market while you're in the area. It is immediately adjacent to Chinatown, and is a funky, youthful neighbourhood that is well-known both as a food market, but also as a great place to people watch, to enjoy a beer on a patio, to shop for vintage clothes, to check its many quirky shops, or buy baked goods at Wanda's Pie in the Sky, or sit in Kensington Market Park and smell the ganja smoke emanating from all the groups of young people picnicking I the grass while families enjoy the playset just a few short meters away. There are even a few marijuana cafes in Kensington. You can't buy marijuana there, but you can smoke it in the tranquil back patio of Roach-o-Rama while you enjoy a chai latte or coffee, taking in the ambiance. I don't know if you occasionally indulge, but even if you don't, Kensington Market is popular for both old and young folks, and is especially lively on the weekends. Its narrow streets, dense shops, residential Victorian towns and rowhouses integrated into the neighbourhood, making it a unique mixed-use market, with homes, shops, a proper food market, but much more. Use the opportunity to rest a bit, sit I the park or on a patio. Because you have more walking to do.
Make the ten-minute walk back down to Queen St, (you can take the streetcar, but the walk is quite short), then walk west on Queen, away from Yonge. You can choose how far you wish to walk, but could feasibly continue all the way to the end of Queen St. at Parkdale's west end, because there is never a lack of things to see and do for its entire length. There are some great diners, eateries, restaurants and bistros west of Bathurst, including some great burger places on the south side of the street. So of you haven't had a proper meal yet, you'll certainly find something you like along Queen St. If you make it to Ossington Ave, take a walk north to Dundas St. West. This area used to be, at different times, filled with flophouses and rooming houses (it was to here that James Earl Ray fled after shooting Dr. King in Memphis, hiding out in one of the many rooming houses until he could forge an ID and obtain a Canadian passport under an assumed name to travels to Europe, where he was ultimately caught), then dominated by the mental patients of the nearby Centre for Addiction and Mental Health, then filled with secretive karaoke bars frequented by Asian gangbangers and other shady characters. Now this stretch of Ossington Ave. has been turned into the densest strip of hip, happening bars, coffee shops, restaurants and bistros, and shops. It's definitely worth a look.
If you make it this far, you will surely be exhausted, and can walk back down to Queen (or stay on Dundas), and catch the streetcar back east to the lot where your car is. You can get off at Church and wal the half-block to the lot. However, here is where I will make my more about parking and how you choose to get into the city. Because parking in the downtown can be expensive, you may want to exit the QEW/Gardiner at Kipling Ave. on your way to the city, and drive north a few minutes to Kipling Station's South Parking Lot. Here you can park the car for free and take the subway into the city, right to Dundas Square where my hypothetical itinerary begins. To get to the South Parking Lot, you simply follow Kipling Ave. north, staying in the right lane. In a few minutes you will approach an arching traffic bridge that can be seen from a distance. You are going to be exiting right onto a short two-way laneway that diverges from Kipling just before this traffic bridge. It is marked it a sign with an arrow that says Kipling Subway Station. Follow this laneway until it ends a few sort meters ahead at Munster Ave. Take a left on Munster Ave., and this will bring you under the traffic bridge and right to the parking lot, where you can park for free on weekends. Simply park your car, head down into the station, where you can consider buying a day pass which will cover two adults and up to five children for $10.75. If you don't like walking so much, and would prefer to take the streetcar to the destinations I mentioned, the day pass is a great deal. And every location I mentioned can be reached by streetcar / subway. It's something to consider.
Finally, in regards to my itinerary...many tourists come to Toronto and visit the best-known attractions, like the CN Tower, the Eaton Centre, the Hockey Hall of Fame, Dundas Square, Centre Island, Yonge St., and perhaps the AGO or the ROM. Other than the CN Tower, which I believe is too expensive and overrated, all of these attractions are worth seeing. However, since you live in Buffalo, you can visit as often as you want (and I promise you will want to visit again and again once you visit the first time), and visit these attractions one-by-one. IMO, as a first-time visitor, I tried to give you an itinerary that would allow you to see a couple of the major tourist attractions (Dundas Square, Yonge St., even Eaton Centre if you want, because it's right there and will take you down to Queen St. so you can enjoy the shopping centre while making your way south to Queen), but most importantly would give you an opportunity to visit a couple of Toronto's most vital, diverse, and unique areas, to give you a small sample of what the city is all about - a small taste of what the city really is. Toronto is a city of neighbourhoods, and its neighbourhoods are its best feature. I've steered you towards some of the city's unique and famous neighbourhoods that offer you a multitude of experiences, from shopping to dining, to people watching, to taking in the diversity and plethora of cultures that make Toronto the unique and amazing city it is. Hopefully, my suggested itinerary will interest you ('cause I've spent like an hour or more typing it

).
Finally, to address your concern about being a mixed-race couple. It's not a concern at all. Toronto is one of the most diverse, multicultural cities on the planet. Mixed-race relationships are not just common - they make up a pretty large % of all the couples I see in the city on a given day. I've been in several mixed-race relationships during my life (in fact, as a half-Puerto Rican white boy with dual American/Canadian citizenship, I've only dated one white girl. All my other girlfriends were neither white nor Latina - so I've only ever dated one person within my ethnic group). The whole racial hang-up thing that can be prevalent in some parts of the US is pretty much non-existent in Toronto, and most of Canada. We are proud of our multicultural make-up, and kids grow up with kids of every race in their social circle. Which is why inter-racial dating isn't even a thing, especially among those 50 and younger who came of age since multiculturalism became Canada's official policy. Toronto is generally one of the most laid-back, tolerant cities on Earth. I think you will see this for yourself when you visit.
Yeah, anyways, my fingers are tired. Please respond, give some feedback. I'm sure others will chime in with their suggestions. There are really so many things you can do. My itinerary is just a suggestion to give you a good introduction to Toronto, its diverse neighbourhoods and its culture. Tell me if you like the sound of my suggestions, or if you have particular interests. Me and the other members will help you out. I promise you, you are going to be blown away by the city, since you've never been here before. Once you realize such a great city is only an hour away from you (don't get me wrong - I love Buffalo, and used to visit all the time), you will want to visit as often as you can.
BTW, you should change your money at your bank before you come. If not, there are places to do it, but it's definitely easier to it there in Buffalo.