I stayed at the Radisson Longueil just three nights ago. It's a decent property, across the river from Downtown Montreal. Free parking and the subway is right next to the hotel. Only 2 stops to Downtown Montreal. The station next to the hotel is more than a subway stop. Not sure where the other trains go to, but it is NOT the VIA station downtown, below the Reine(Queen) Elizabeth Hotel. That is the Station where you take the train to NYC or Toronto, etc.
There is NO Radisson downtown, so I imagine the Longueil is the closest.

If you're a Starwood member, the Le Centre Sheraton is just a few blocks from VIA. The 4 Points is a short cab ride away, and the rates there are VERY reasonable. I just paid $77.50Can for the other two days in Montreal. I don't like to stay more than a night at a time with Radisson, as there is no point incentive to do so.