I went to Montreal on holiday about 8 years ago and stayed pretty close to McGill as my sister was spending a year working there. City is really pretty and there was loads of stuff to do there as a tourist (parks, cultural and historical stuff, zoos/aquariums, good cafes etc.) Though I've heard people there can be pretty insular and dislike English speakers most people seemed really welcoming and nice.
One thing that is not so nice is the climate as it was around -15°C in October when I was there and it gets down to around -40°C in the winter. However they do have an underground set of streets that are heated so you can get around without freezing. Also it didn't feel as cold as the UK when it gets below freezing because it's not as damp.
My sister spent half the year there and seemed to really enjoy it but had to come home in January because she couldn't cope with the climate.