Chateau Champlain is a much larger property, full-service with a bar and restaurant. Closer to downtown (couple of blocks to Ste-Catherine St., the main shopping street).Golds and plats (and their friends?) will get access to the CL. Maybe plats will get an upgrade.

Springhill Suites is in Old Montreal, nice but basic, great location for exploring the Old Port, everyone gets breakfast (pretty good) but there is no restaurant or bar on site - lots close by. No particular benefits for golds and plats (except for arrival gift). No upgrades.

Either location offers good restaurants in walking distance. Popular bars in both areas but maybe more downtown. Rather than basing the choice on benefits, you might be better off to decide what you want to do out of the hotel and go from there.