The whole experience went like this - drove up to the valet lot gate, there was a minivan parked across it, guy gets out and starts telling me "their systems are down" so I can't park. As he's doing that another guy comes zooming up behind me in a white truck with a plough, jumps out and starts ranting to me that I have to move, they're full and I can't park there. When I tell him I have a reservation and show my printout he literally yells "that means nothing, you have to park somewhere else". I tell him that sucks and he doesn't need to be a dick about it then he storms off to his truck and zooms off. Other (chill) guy apologizes and we leave.
Having got two reasons why we couldn't park, I suspect the one from the nutcase is the right one - the lot looked jammed as we drove around the corner - vehicles double-parked and crammed in every available space. My guess is the booking system isn't linked to available spaces in any way and they routinely overbook on the hopes they can cram cars in somewhere.
Needing to get my family to the Caribbean and now having to go get the car charged before I leave it a week, the last thing I had time to do was start calling or going online to complain - not going to let them waste any more of my time. Their online experience is decent and the services sound great, the on-the-ground reality in Montreal is they suck, or at the very best are a big gamble, with some questionable staff who'll have the keys to your vehicle. I won't rely on them again.