Well, it depends on you-
-Botanical Gardens with Insectarium (that's what it's actually called)
There's also the Saint-Lawrence Valley Ecomuseum dedicated specifically to birds, mammals etc; around Saint Lawrence river, similar to the BioDome which I mention later.
- Go to a nice restaraunt, or an old carriage ride, in the Old Town
- The BioDome (there is something similar called the BioSphere, very boring, nothing for adults etc;!) great if you are an animal lover, definitely.
- The old Olympic Stadium thing (you can go up really high on this weird lift thing after being inside it, and see all around Montreal which is great, and its easy to walk from there to the Botanical Gardens, if you want to)
There's also a few museums (Montreal Rail Museum, Montreal Museum of the Fine Arts, Museum of Archaeology and History, the best one I remember was Sisters of St Anne Historic Centre, definitely good if you like history or anything, although if you don't, very boring!)
There's also things like taking a trip out (very easy to go there by the way) to the Laurentian Mountains, which can be amazing.
Somewhere is the Chinese Garden, which was good, and I think there's the Japanese Garden in Montreal too.
There's a lot of Basilicas, and cathedrals all around too, too many to list, but the best ones to visit would be Notre-Dame Basilica (I think Basilique de Notre-Dame) or St Joseph's Oratory on the Mount, but I don't like that kind of thing, so haven't much experience or anything.
Food, they have a Chinatown which has great food, and there are restaraunts dotted all around the Old Town which are easy to find, especially near the Old Town docks.
Nightlife, Rue Saint-Laurent is good, some bars too. Rue-Sainte-Catherine is a nice place by day, with a number of nice, small restaraunts, but its not the best place to go after dark.
If you travel before March 24th, then a must is the Snow Village It's amazing to visit!