A judge will "likely" order you to contribute your proportinate split based on your income.
You state he's been playing for many years at the AAA level so there is status-quo and if he's 16 and playing AAA he's probably very good at it.
I'm guessing the yearly cost is probably around $4,000 - $5,000 if you are in or around the GTA area. You'd likely be ordered to pay towards, registration, team fees, equipment. You probably won't be on the hook for hotel costs if your ex is the one who takes your son to tournaments, etc ...