We stayed at the Hotel Saint Sulpice in Old Montreal after our wedding 11 years ago. It was lovely. It's a smaller boutique hotel on a side street. I haven't been back since but it still seems to get good reviews.
http://www.lesaintsulpice.com/
Tons of nice stuff to do in Montreal in the summer. Once you know your dates, check if you will be there for the jazz Fest or the comedy fest. Both are lots of fun. I can't remember the name of the street (just know how to drive there) but there is a large area only for pedestrians with street performers and all sorts of restaurants and cafes.
http://www.montrealjazzfest.com/default-en.aspx
http://www.hahaha.com/en
DS - 10
DD - 8
Twin Girls - 6