A Passport is ALWAYS the best alternative. As a US citizens with lots of family in Canada, we travel there every few years. The first trip after my son was born, when he was 2 1/2, we traveled with Passports for us and birth certificate for him. I wrote the Canadian Consulate in San Francisco, and they replied this was fine. Canadian Immigration in Calgary didn't agree and chewed us out for not having a Passport, but did back down after I showed them the letter from THEIR consulate. They said they had no way of knowing whether this child was really ours without a picture ID. However, as soon as we got home, we got him a passport, and when our daughter was born, we got one for her when she was two, before a trip to Canada. We have NEVER had a problem with Passports.