It might be more cost-effective in driving from Buffalo to Niagara Falls (USA side) instead of taking a train. It's only about 20 minutes drive(1) via the Grand Island bridges.
From downtown Buffalo, take
the 190 North (through Grand Island) (2) and get off at the Robert Moses, follow that all the way into the city of Niagara Falls, and follow the signs to get you to the Rainbow Bridge to cross the border into Canada.
Staying on the American side, the hotel at the Seneca Niagara Casino is great, there is a seperate enterence voiding the casino gaming floor (if it's desired not to gamble), a little pricey, but it's a higher class hotel... and always clean. The Casino is about 5 minutes from the Falls park area, which is where the Rainbow bridge is.... you can visit both sides of the Falls in one trip, and yes, you can walk over the Rainbow bridge border (3).
This picture gives an idea of how close the USA & Canada are, that's the Rainbow Bridge. It's less than a mile.
As per asking about what to do on the American side, I created a post of pictures of my day at the Falls. It is beautiful on the American side.
Click here.
Hope this is helpful. Enjoy your trip.
(1 depending on traffic/rush hour)
(2 there's a $1.00 toll charge in each direction)
(3 make sure you have passports/current US identification readily available)