but you can't miss a good smoked meat sandwich from Schwatz'shttp://www.schwartzsdeli.com/
and you must try the bagels in Montreal, some say they are nicer than NY bagels. The best in town are St Viateur Bagelhttp://www.stviateurbagel.com/
Don't forget to have poutine, but I'm afraid I left Montreal 16 years ago so I can't really tell you where the good ones are now, you might want to try at Lafleur.
Enjoy your stay in Montreal.....I miss my home town terribly!