All American (and other international travelers) must carry acceptable identification when entering Canada. A passport is required since it's the only reliable and universally-accepted identification document for the purpose of international travel*. Additionally, while American travelers can presently enter the U.S. or Canada up until the day their passports expire (Government of Canada), as a general rule, passports must be valid for six months beyond the date travelers will exit the United States (U.S. Customers and Border Protection), which is highly recommended as a precaution. If you need to renew your passport (or apply for one), please do so early. Visit the official website of the Government of Canada or the U.S. Department of State's Bureau of Consular Affairs' website for more information on traveling to Canada.

*A border state enhanced driver's license is valid for land and sea entry only and may not be used when traveling by air.