I should pay more attention.
I was born and raised in this great city. I encourage all to make the trip. Lots of fun. And OP, feel free to PM me with specific questions.
To touch on a few things mentioned above - Schwartz's - a Huge yes. Fantastic and Montreal-only. Smoked meat is a offshoot of the pastrami/corned beef world but it's own wonderful thing. The Main, as a substitute. No, just wait it out at Schwartz's; it is worth it.
Poutine - everywhere you can get it will be a treat

For more info,
http://www.montrealpoutine.com/reviews.html?reviewsRight near (across the street?) Schwartz's is a hipster bar/hangout called Le Bifteck. To give you a sense of it (or at least how it was over 10 years ago, when I still lived there), Melissa Auf der Maur (pre-Hole etc.) had her own chair there...
As noted above, some of this may be years out of date, but some thing rarely change.
St.Laurent is the anglo hipster street, crescent street area is the angle "meatmarket" scene, st.denis is franco-hotspot (or one of them). Definintely go explore Mount Royal park (in the day). It is very pretty and usually something fun going on. I would agree that the Art museums are nothing special and the Architecture museum actually is.
Old Montreal is great area to wander around in the evening, and despite some touristy trappings still a must.
The Mirror (
www.montrealmirror.com) is a great resource for local entertainment listings, take the restaurants recommendations with a grain of salt (look who's advertising!).
The subway (Metro) is easy to use and should be able to take you anywhere you want to go. It does not travel througout the island but you almost certainly won't be going where it doesn't go.
One sorta unique thing to recommend is to go see a band in town, but you probably won't have the time given the Just for Laughs activities. Local bands are always entertaining but if some band you like is on tour and happens to be in Montreal at the same time as you, great, the local clubs are for the most part great and the audiences are comparatively (to NYC, for example) small.