I do not live in Montreal, I do not know of anyone who offers classes and I do not teach the theremin myself. Nevertheless, let me offer some advice.
The theremin is unlike traditional instruments in that there is no established method of playing it. If you wanted to learn the cello or the concert harp, just about anyone who has been playing for a year or two could show you the basics. Not so with the theremin. Most thereminists are self-taught and no two play exactly alike.
One of the problems this has created is that with no competent teacher to oversee their progress, many budding newbies have unwittingly developed habits that later interfere with their ability to advance. This can be very discouraging and is one of the reasons why the dropout rate is so high among thereminists. While there is no "right" way or "wrong" way to play, there are approaches that will help you get where you want to go and others that will hinder you.
I suggest you carefully study videos of the theremin player you most admire, and strive to imitate the technique as closely as possible. Keep doing this until your own particular style begins to assert itself spontaneously.
CARDINAL RULE: Never take any advice on how to play the theremin from anyone whose theremin playing you have not heard or do not enjoy.
"The theremin is the most difficult of all musical instruments. It is much harder than the violin, which I played for years." Clara Rockmore