We recently stayed in Old Montreal and found that it was walking distance to Chinatown, where we ate most of our meals, great restaurants and not expensive, and also were able to pick up some cheap fruits and veggies to snack on.
We found that we really did not need a car in Montreal, wonderful transit system. And this is coming from someone who hasn't used a bus in years, we have a very poor transit system where I live, plus I live in walking distance to a lot of things, and had never been on a subway.
I found Montreal to be very friendly and would love to go back again. Enjoy your trip.