We stayed at the Sonder with another couple. There were some stairs to go in, but there might be a service entrance--if you are in need of a ramp I suggest checking with the manager before reserving. The apartment was exactly as described--clean, comfortable, excellent location in Old Montreal. Nice mattresses, bright windows, a Bixi bicycle stand right outside and a subway nearby: a perfect base from which to explore Montreal.
While we were there the smoke alarm went off, and everyone evacuated! It turned out there was a fire in a trash bin in the alley next to the building. We were quite impressed with the sprinkler system--this is a very firesafe building! And a Sonder employee appeared within minutes to see what was going on and communicate with us. He reset the alarm system when he knew it was safe. Afterwards, we received a text apologizing for the disturbance. None of it was their fault, and they could not have handled it better.