You are in a tough spot about her possible move to Canada and taking your child!
I do believe that fathers should financially support their children, and especially if the mother does not have a income to meet the children's needs....and in your case, your mother & brother are partly to blame for her not having a FT job, I think. Anyway, I would not jeopardize the child's welfare for any relationship......marriage, friendship, or otherwise. My advice is to get legal assistance (at least advice on where you stand). If you have joint custody, I don't know if they could haul her back from Canada or not. In fact, don't act on "anything" until you talk to a lawyer.
As for the people who do not support her decision, you have to realize that she has chosen this route over staying M to you. You care very much that she is alone, don't you? There are some things you can't protect her from experiencing....and as hard as it is, you shouldn't. One of the hardest things for many men is to not rescue the one who left him. She has to put those BG panties on!
I am so sorry you are in this sad situation.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!