Now that I've been here long enough, I've had a lot of time to reflect on the uniqueness that is Montréal. The bilingual discussion has come up in several classes already, mostly in Conversational French and Cultural Immersion Through the Fine Arts (I highly recommend both! Great teachers and an awesome opportunity to expand your knowledge of language and get out and about in the city).
Most of the city is bilingual, so you won't have a lot of problems navigating around or communicating. However, a little effort in speaking French goes a long way in gaining the esteem of Montréalers. They always appreciate the effort, and, like my Advanced Seminar in Game Design teacher has told me, you can get by in this city just speaking English, but it'll be that much harder to fit in. Even if you think you sound stupid, people will just smile and answer you. It's the effort that counts, even just saying “Bonjour, hello,” instead of just “Hello” shows that you acknowledge the duality of the city.
It's great now, though, because in general people can speak to me in French, and I understand enough that I can at least respond to them in English without them having to translate. Just being in the city did this for my sister, who was up here last semester, but I think the Conversational French has pulled me far ahead in understanding. I still occasionally blank out, but that's okay. “Bonjour, hello” to the rescue! Haha.
It's great that the city is so adaptive and can hang on to its roots in both English and French.