I've never stayed in an actual Montreal hotel.
When I wasn't leased up, I stayed at the YMCA, and I'm not sure daughters could stay there.
As far as I remember, the best hotels are between the Metro (subway) stops of Guy-Concordia and Place-des-Arts on the Green line.
(I could be wrong, but I spent on a lot of time walking around there, and there were plenty of tourists and hotels.)
There are lots of restaurants in that area (centered around Crescent and Ste Catherine) below Sherbrooke St,
and also nearby on Saint-Laurent and Saint-Denis streets above Sherbrooke St
(with more francophone tourists on the latter two streets).
All of this is a long way from Olympic Stadium
I don't know for sure how late trains run.
(But see: http://en.wikipedia.org/wiki/Montreal_Metro#Operation