MUST. VISIT. LOCATION. IN. MONTREAL.
I don't care what your time constraints are. Just go.
Make a meal out of it!
There's a really good gelato place. The fruits are yum at this farmer's market (it's been claimed that Jean Talon is the largest open air farmer's market in North America). I'm not sure that I can confidently say it's the largest, but it's definitely one of the best. It's my fav. My 2nd fav would be in Portland on the PSU campus.
I've also had bison meat on a stick here. Quoi? Oui!