Don't mix up the badminton at Guy Favreau...The times listed as "open badminton" are actually classes. You can play any time, however you must reserve a court 48 hours in advance. I have never showed up randomly so I don't know if some people let anyone play, but I will be going in the next few days. Should be better levels than elsewhere... I am C level and most places suck lately.
There's a Montreal Badminton group on Facebook called Badminton 514, they organize dropin games every Tuesday starting 7:30 PM I think. The problem is that most people go there for fun and to socialize. Apparently they do have another gym reserved for advanced players but you'll have to contact them to find out.