Yes it will be about 2yrs if you have to start all over.
I'm going to be straight with you here. You are the parent. You already have the court order to allow the move he is 13 no way capable of making a choice like that. Why is he getting so much say about the move, again you are the parent.
Talk to your son about all the things and new places he can see. About giving school a chance, life in the US a chance and if he gives it an honest go then you can apply for re-entry permit after he gets his GC, to allow him more time to stay in Canada.
If your ex is pulling this stuff just think of what he is going to tell your son after you leave without him.