Unfortunately, no such group exists right now. You have the Teacher’s Alliance of Montreal of the CSQ (Alliance des professeures/professeurs de Montréal – CSQ) but there’s no gay or lesbian chapter in that group. The CSQ (a labour union) has a Committee on gays and lesbian rights but you have to be a member of that union to participate in that Committee, it’s not based only in Montreal and it’s mainly francophone.
You have three choices: you can ask your teacher’s labor union in your school to get affiliated with the CSQ (Centrale des syndicats du Québec) so that you can participate in their gay and lesbian committee, you can try to talk to the Alliance des professeures/professeurs de Montréal so that they create a gay and lesbian chapter or you can talk to some teacher colleagues about creating your own Montreal based teacher’s association.
If you’re interested by the CSQ Committee, here’s a link to their webpage (hope you understand French!)
Have a good day!