As a Marriott Titanium member and AV technician, I've seen various aspects of many Montreal hotels. Even did some mattress runs in many of them.
I love the Marriott In-Terminal Airport (slept 3x, worked on conference level a few times). Fun pool and allows to watch planes zip by the window taking of from the southern runway. They don't give automatic suite upgrades, so ask for it as an elite.
Worst hotel in town is the AC Hotel. We found our bed used upon check in, bathroom was disgusting. This only months after opening. It's the only hotel I've ever walked out of before spending the night. Courtyard next door belongs to the same owner, but I've never had a room there. Great views at the Courtyard though, but not the AC.
Marriott Chateau Champlain is undergoing major renovations. I've always gotten a suite upgrade upon asking (they don't automatically upgrade elites.) When the lounge is closed, breakfast buffet in the restaurant, but it's a whopping $11 to upgrade to warm buffet!
The Delta I love as well. Fun resto-bar that is rarely crowded. No suites that I'm aware off (except maybe one Presidential Suite, which is never shown on the website, but I've seen on the floor plan and seen hints of while walking through the service corridor behind the club lounge.) Great breakfast buffet in the restaurant when the lounge is closed (weekends and holiday periods).
Haven't slept at the Renaissance, but the roof bar is nice. It's also where (awkwardly) the small pool is located. Can get a real party scene on weekend nights.
I have more extensive reviews on some of them on
Marriott Insiders.