There are 2 RIs in Montreal, sort of. The Peel one is in the downtown core but the Westmount one is not too far from downtown (less than 20 minute walk to Peel - 1 more stop on the green line to Atwater). It would be very pleasant to walk in May.

I don't know the hotels. I almost think that for a family of 4, the Westmount one might be better. It used to be an apartment building so I would think the rooms would be larger (and it seems to have a pool). The photos seem to show it is one generation older than the Peel one. It is a tall building so I think the view would be better - from the photos, it seems the pool and gym are on the top level of the building and the view is pretty nice.

I would think all the rooms in Residence Inns have stovetops but better ask to be sure.

Food/groceries would also be easier in Westmount - there is a supermarket inside Place Alexis Nihon and plenty of food in the "Concordia Ghetto" (actually I don't know if they call it that - there is the "McGill Ghetto" east of the campus). Food (and everything else) is a lot more expensive in Canada than in the US.