The father is Canadian and moving back there, and is threatening to sue to change the original visitation agreement...

Five months ago, a friend of mine was granted her divorce after 10 years of marriage-she's a United States citizen since birth, he's Canadian, and never gave up his citizenship while here legally) She has custody, and because he is not financially stable, she did not seek child support. Her ex has visitation every other weekend and 6 weeks of summer. He has just told her that he is returning to Canada permanently because current girlfriend is 5 or 6 months pregnant and he doesn't want to deal with the situation. He also informed her that he's going to be suing to change the agreement of the original agreement regarding visitation (he wants to have child with him in Canada from day he gets out of school to day before he starts in the fall) and more holidays/school breaks, and he wants her to bear the expense of transporting the child up there and back. Much of this stems from his ire over her starting to date again. Given his current situation and his reason for returning to Canada, is it possible that he will be successful in having the original custody arrangement changed? Are there any websites regarding International Custody Law that we can look into? Thank you very much for any help you can offer.