In that case she can't sponsor you but it's possible that you could get a work permit, even if you are low skilled. You need to find an employer who will apply for your labour market opinion and then you can apply for a work permit. It's not guaranteed to be granted since they are not supposed to give you a temporary permit unless they believe you are planning on going back to the US and with a fiance and children in Canada, they may find that unlikely but it's worth a try. With you working, you may be able to get your wife off welfare and then she could sponsor you. The other option is like you said, you go back to the US and sponsor her there.