I have been often in the Ritz-Carlton for work (events) and it is definitely a hotel that lives up to its reputation. Your old-SPG-now-Marriott card may land you points, if you're still in that program, however elites don't get club access for free.
Haven't really been in any of the guest rooms, but I would presume that they are as kept up as the rest of the hotel. It's one of the oldest hotels in town, definitely a flagship of the RC brand (actually the only RC that is independently owned and operated).
The Four Seasons is brand new and definitely has a more modern touch to it. Last time I passed by, it still wasn't 100% open yet.
I see you're Hyatt Plat, which is too bad: the Hyatt closed a few months ago to be re-opened as a DoubleTree by Hilton.
If you'd like other hotel suggestions in Montreal: let me know. I have experiences with plenty of them, although mostly the Marriott-affiliated properties.