We stayed for two nights in Montreal as the mid-point in a two week road trip. The hotel itself is easy to find as you enter Montreal and as we had a car we'd booked into the hotel's car park for the two nights.

And here-in comes my first tip! You need to check-in first before you can access the garage. There are waiting spaces (15 minutes) outside the hotel where you can leave your vehicle whilst you complete the check-in process as you will need your room key to gain entry to the garage. The garage is underground and has low headroom (5' 6") and the spaces are very tight! Parking charges are CAD$20 per night.

Check-in process itself smooth and efficient handled by friendly, helpful staff (we got maps and loads of tips - for good places to go within easy walking distance - from the young man who helped us).
Our room was large, with a fully equiped kitchenette. The bathroom was on the small side with complimentery toiletries but the towels were on the small side. One observation is that there was no in-room safe. Again there was free wi-fi available in room. Bed was comfortable; one thing I found strange was that the duvet was placed between two sheets rather than inserted in a duvet cover. Not sure how I felt about this as I wasn't sure if the duvets themselves were changed at each guest change or just the linens. Either way a good nights sleep was had, and there was no external (or internal) noise intrusion.
We were booked in on the bed & breakfast rate. The breakfast was so-so nothing to rave about with limited choice - but ok for a coffee and pastry before heading out for the day.

When checking out, if you've parked your car in the garage, you'll need to remove it first as again you need the room key to exit the garage and there is no release mechanism from reception!

We reached the hotel pretty late on Christmas eve and the attendant at the reception was extremely cordial and even gave my niece a little candy. Small things like this make you feel so welcome. She also gave us some tips for sightseeing for the next day.
After this we went to the room which was very clean and comfortable. The reception recommended a restaurant that was very good and delivered food to our room. The next day breakfast was very good with a nice spread of items. The metro stop is only a block away which was very convenient.
Pros- Awesome staff, clean, great location, onsite parking, close to the metro
Cons- Parking might not be convenient for SUVs. The height is very low.

The also let us keep the car till end of day the next day. Infact we left for quebec city at 10pm, so it was almost 24hrs for us which was great.

I booked two nights at this hotel this week.
Pro's -
location is great, steps from the Alexis Nihon mall, two blocks from st catherine, atwater station
breakfast is included, decent enough to satisfy most travelers for sure
onsite parking (the marriot champlain has but its less convenient, the downtown marriot does not so you must source this offsite)
staff - cudo's to mgt for the reception staff, arnaud was great
Gym was small but nicely outfitted with a penthouse view of the immediate area
Neg's -
Really not much, slightly removed, but I walked to the heart of st catherines in less than 10 mins
Parking is provided, but it is the lowest overhead I've seen in North American. Beware if you have an SUV, 5'6" I think. Charge was reasonable
good luck finding your car too, the elevator only shows P2 but there are 5 levels or so, so you will have to pull your bag along for a ride... bit odd.. but better than sourcing parking offsite

Hubs and I picked this hotel based on its proximity to the Museum of Modern Art, and on price. It was priced well below other similar hotels in that neighbourhood, so we booked it. We were extremely pleased with our choice! While this hotel won't bowl you over with its exterior looks, don't be put off by that. The location is fantastic! Ste Catherine street is just a few blocks walk, as is Concordia, McGill and the Museum. There are lots of depanneurs and grocery stores if you want to stock up on food and/or drinks. All sorts of restaurants are nearby. You can just park your car and never need to use it for the duration of your stay. And while you are right downtown, the street is actually nice and quiet with very little street noise.
Our room was very clean and had all the amenities we needed; a lovely kitchenette (with granite countertop, convection oven, full fridge, dishwasher and of course, dishes), a big flat screen TV, free wi-wifi, a generous balcony with lovely views, a really comfy bed with lots of pillows, and windows that open! (this is a must for me!).
The service was perfect. Checkin was quick and easy as was the checkout. When we first checked in, the front desk staff phoned us to make sure we were satisfied with our room. What a nice touch!
There is convenient underground parking available (for a fee, of course) which was really handy. Please be warned though that it will only accomodate vehicles up to 5'6" in height!
I have very little to complain about with this hotel. The only improvements I can think of would be to have recycling bins in the rooms and also to accomodate adult only times at the pool. Unfortunately their pool, while nice, is quite small and of course very popular with families. All it takes is 2 or more families with young children to use the pool at once and well, it's just mayhem with kids screaming and jumping in and out of the pool. It was not very pleasant.
We didn't eat breakfast at the hotel so I cannot comment on that.
All in all, the Marriott R.I. made our last stay in Montreal very pleasant and I would not hesitate to return to this hotel for any future visits to this marvellous city.