When in Montreal, why not have poutine!! Only if your group likes poutine of course.
Every time I'm in Montreal, I've always stopped by this place. It offers a variety of poutine with vegetarian options, and it's 24/7. What more can you ask for! Personally for me, the portions were really big, even when you just order the regular size. Then again, it could've just been filling.
There's also the 'healthy' options (aka not poutine) for those of you who aren't a fan of gravy on fries. This surprised me when I had a friend who just wasn't into it.