If you are staying downtown, or near to a subway stop, I would reconsider the rental car. Driving in Toronto is awful - too congested and too many aggresive drivers. Pretty much everything to see as a tourist is downtown, and easily accessed by foot, or TTC. And in the downtown area, it's often faster to walk than drive short distances, or grab a bixi (bike share). I'm in Toronto, send me a pm if you want some suggestions of stuff to see and places to eat.