I and my son are in the US, and I'm going to get sole custody of him. His mother (ex-girlfriend) lives in Canada. I want them to know each other, they deserve to be a part of each other's life. If my son and I go to Canada to visit her and her family, will Canada recognize that I have custody, or will she have parental rights there?

I'm especially nervous about her and her mom trying to run off with him.

If you have a court order ensure that you carry/pack it with you every time you visit Canada. I can not imagine how the court order wouldn't be enforced there just as it is in the United States.

Hopefully someone will come double check, but I would think that besides having the legal document, Canada is a neighboring country.