I recently stayed at this property for the first time.  I found the hotel to be a fairly typical North American Westin.  There was nothing to wow me, but the hotel did not have downsides that would prevent me from returning.  If you compare Starwood options in Montreal, the best comparison price-wise, point-wise, and location-wise would be Le Centre Sheraton (both are 12k starpoints per night). I think the choice especially for platinums would be whether you want a hotel with a club lounge or not.  The hardware and the room at Westin is better than Sheraton, but you won't get a club lounge at Westin.

As the platinum benefit at Westin you need to choose between breakfast or points - you cannot get both.  I chose points so I cannot comment on the breakfast quality.  As others mentioned, platinums also get a voucher for one free drink or one free tapas for use between 5pm and 7pm.  Timing was not working for me so I did not use my voucher.

Valet parking is on the expensive side at 34 CAD.  

Room

I booked a traditional room and I was upgraded to a premium room.  I am not sure why they do not call it a junior suite, because the living room is actually completely separate from the bedroom.  I did not particularly like the layout if you are travelling alone.  The room is long and narrow with windows only at the very end (in the bedroom).  That means that when you enter the room, you are in the living room and it's dark with no natural lighting which made the living room kind of depressing.  On the flip side, since the living room is completely separate from the bedroom, you can close the door and you are further removed from the hallway so you cannot get disturbed by noise outside your room for sure.  In addition, the living room has a sofa-bed so I could see that for some people this layout would be convenient if you have a guest or two who want to stay overnight in your room, or if you have children.  You have some privacy because you end up having effectively two separate bedrooms.

The bathroom is nice with a large shower.  As in other Westins, I appreciate the small lavender bottle by the bedside.

Location

The hotel is perfectly located right in front of the convention center and in front of a subway station (Place d'Armes).  You are only a two-minute walk from the W so location is pretty much the same.  This area is close to the entertainment district and the business area so it is easily walkable to most locations and a big plus for this hotel.  

Overall

I usually prefer hotels with a club lounge so I will be hesitant to pick the Westin instead of Le Centre Sheraton in the future.  However there is nothing wrong with Westin and I think it comes down to personal preference.  For sleep quality and a quiet room, Westin would be a good choice especially in the premium room.