Reporting back for YOW-YYZ: I arrived 2 mins after the cut-off for the flight I wanted, but the agent was still able to check in my luggage (since my originally booked flight was still open for check-in) and put me on standby. Unfortunately, since I'd arrived after the cut-off, the gate agents had cleared the party of 2 on the standby list, and so, while I was #1 on the list, I did not get on the flight. So the take-away is that it's at least possible to be put on standby for a flight you've missed the cut-off for, even with luggage.

I'd be happy to hear that it's possible!