I don't know about Montréal, but it seems to be a pretty open area to me.

As far as the gaydar goes... false alarms will happen and goodness knows I've always convinced myself into thinking someone was gay because of wishful thinking.

Just share interests, I guess. When I want to find out if someone leans a certain way, I bring up a generally well-received topic with some gay leanings--for example, asking a girl if they like Tegan and Sara, then going to topics that are a bit more niche. That's the most casual way of going about it, I've found.

I'm in Southern California; there's lots of lesbians around here of all types. I still get surprised by who I find out is actually gay. The nerdiest of nerds and the femmiest femmes. And I consider myself to have a decent enough gaydar, haha. Most people tend to reveal it after some conversation, really.