Why walk when you can ride? I picked up a Bixi Bike and was pleased with the performance. It feels almost exactly like the same Boris Bike that I rented often in London. Solid ride, three gears, good brakes and wide tires to eat up the bumps of a city road.
The rental system is the same as London, where you swipe your credit card in the machine (it accepts 'swipe and sign' cards and probably 'chip and pin' cards too) and you pay a basic daily rate and then more depending on how long you keep each cycle. The first half hour is free.
Machines are scattered throughout the city so you are never too far from a place where you can pick one up or drop one off.
Tip: Montreal is a big city. Get a helmet and save your noggin, mkay?