Well that's a pretty broad question, but I'll try my best.
First off, a staple of any Torontonian's diet is street meat (AKA vendor dogs). This is a good place to start. But don't skimp, spend the extra dollar and get a sausage, you won't be disappointed. If you want to get a little more ethnic, try Gandhi Roti on Queen West or Ali Baba's which is a chain that you'll find all over the city. Or just a few minutes away you've got Burrito Boys. No matter what you feel like, GET THE HALIBUT BURRITO! I hate fish and I still say it's the best burrito I've ever eaten. I'm sure you weren't thinking burgers, but I would still highly recommend trying either a Dangerous Dan's or Hero Burger while you're here. Again, no disappointment guaranteed!
Now if you want to class it up and spend a little more money you should check out the entertainment district on King West. There are tons of nice places to eat, and plenty of cultures represented. That's where you'll find the best of the best. You'll pay an arm and a leg for it, but it'll be worth it.
I could name a million more, but that's a good place to start.