Try, in no particular order:
CN Tower (on a clear day!) worth it for the view.
Niagara Falls.
The Sky Dome.
Take a look around Chinatown and see some of the weirdest foods you've ever seen!
If your feeling intellectual try the Royal Ontario Museum (ROM).
If it's sunny, visit a neighbourhood called the Beaches.
The Harbourfront
Toronto Islands (city park on islands in Lake Ontario, great views of the city).
Take a walk along Queen Street West - lots of funky shops and bars and stuff - and check out my old apartment at 759 Queen Street West, it's the one with the pink roof!!!!!
Hope that helps, it should fill, a day or two anyway!