Why do you need a passport to go to Canada?
Passport is not required to visit but is recommended. Generally speaking, the US is actually pickier than Canada in this regard meaning it is easier for a US citizen to get into Canada without a passport than it is for a US citizen to get back in the US without a passport. Customs people are not trusting by nature. The fact that you know youre a US citizen means nothing to them without proper documentation. Determine your eligibility - What you need to visit Canada as a tourist