Hehe, I am from Montreal.
For unique shops, head to "Les Cours Mont Royal" located next to the PEEL metro. There you'll find stores like
Space FB (showcasing local talent Francois Beauregard-they're having a HUGE end of season sale right now, everything is 50% off or more),
Giorgio Femme (located on the before-last floor) that carries brands like Lanvin, Balenciaga......
If you are looking for trendy clothes head to
StyleXchange also located in Les Cours Mont Royal or
EnrXchange which carries Fornarina and Miss Sixty jeans at hard to beat prices (85$ for Miss Sixty jeans and 65$ for Fornarina!!!!!!!!).
For vintage finds, head to a
street called Mont Royal, (it's in front of you right after you exit the Mont-Royal metro). Turn right, and you'll finds tons of shops (from CDs to jewellry to vintage clothing.......).
For "casual" shopping, go to metro McGill (downtown!), there's an underground shopping mall there that links to thousands of shops in tons of shopping malls (Centre Eaton, Complexe Les Ailes, Place Montreal Trust, Carrefour Alliance, Les Cours Mont-Royal, Place Ville Marie.........................). The best stores to check out are
Bedo (on St Catherine street) which is from an excellent local designer (his stuff is like Marc Jacobs meets Zara) at very attractive prices (20$ to 150$) and
Holt Renfrew (which carries designer clothing), it is next to metro Peel.
If you have any questions, feel free to PM me.