You have to apply for Canadian citizenship for your child after he or she has obtained US citizenship natually by birth. My colleague has a sister who was born in the US, but she owns Canadian citizenship as well from parents. He said US authority didn't want to give her US passport initially and it took a great deal to finally get it. It's OK if you don't apply for Canadian citizenship for your child, but I know Canada school boards don't accept foreign students. You can apply for permanent resident for your child instead of citizenship.