Your best bet is to use an ATM and withdraw Canadian cash- you get the wholesale rate on the exchange. If you have an account at a large bank, see if they have a branch in TO- they might have an ATM near you that will be free.
Be careful using credit cards- some will charge you a foreign transaction fee- can be as much as 5 bucks every time you use it. Try to find out about this ahead of time or just don't use the card. Card companies are big on fees these days.