Great city. Check out old Montreal, St. Catherine/the area around McGill is gorgeous. But the most important thing of all is to eat POUTINE.
I used to live in Place des Spectacles, right next to Place des Arts metro and the huge Jazz Fest enclosure. You probably know about the festivals and all the other stuff they pump to visitors, so let me highlight some underrated parts of Montreal: Bouillon Bilk has GREAT duck, mussels and lobster, and is hands-down the #1 restaurant in Montreal for my money. Kazu (near Concordia) is great Japanese food, though there's always a lineup. You'll want to go to "no-name" bar for the best Old Fashioned in the city. (Bar 5295). If you're trying to go more for a Yuppie ambiance, Furco or the lounges in Old Montreal are what you're going for. Hipster bars = Plateau (especially around Rosemont station). Partying with trashed out American/college girls = Tokyo Thursdays or almost anywhere in St-Laurent (it's an infestation). Apt. 200 is about the only classy place on the joint. If you're going for more of a laid-back family ambiance, stick to the Irish pubs on Crescent. Crescent is the Anglophone party street (boring, good quiet place to knock back a pint). St-Laurent is the multicultural, Francophone party street (wild, unpredictable, closer to what Montreal actually is these days). Every vice is reasonably easy to score, you just have to make friends in the parties you go to--if that's your thing. Late night eats: Boustan wraps. And poutine (La Banquise has the greasiest). Must see: Mont Royal in the early morning, Tam Tams on Sunday, Place Ville Marie has the best rooftop view of the city (though I'm not sure if it's open anymore). Enjoy, and pick up a little bit of French along the way--cela va t'aider.
What the others said, plus I really liked the food in Little Portugal. I also had the best burger ever at a place called Burger Bar on Crescent street. Get the "Hangover Burger". Massive amounts of poutine and a fried egg on a bacon cheeseburger, comes with fries and a salad. Wasn't too expensive either if I remember correctly.
