This is well known all over. I didn't come to Montreal specifically for it, but thought it would be nice to hear a little music while I was there.
I got the events schedule and wanted to listen to a band that was playing at a convenient time for me. When I went there, it was standing room only. The band was playing for an audience, but there wasn't much sit down space. And in Quebec it appears that people can smoke wherever they please. I started standing while the band was playing, but there was no escaping the smoke unless I were to leave. So that is what I did. It is too bad as the band was good. My suggestions to future organizers would be to have more seating even for the smaller shows and to have designated smoking areas if that is possible in the province.
As an aside, the random street performers were entertaining. Some... a bit strange... but fun altogether.