Canadian citizens travelling by air to the United States must present one of the following documents: a passport, which must be valid for the duration of their stay. a valid NEXUS card, used at self-serve kiosks at designated airports.

For the vast majority of travelers, the answer is no; you cannot fly from Canada to the United States without a valid passport. Under the Western Hemisphere Travel Initiative (WHTI), all travelers—including Canadian and U.S. citizens—entering the United States by air must present a valid passport or a specifically approved air-travel alternative. The only major exception to the passport requirement for air travel is the NEXUS card, which can be used at self-service kiosks in designated Canadian airports with "Preclearance" facilities, provided the traveler is a pre-screened member of the program. It is important to note that "Enhanced Driver's Licenses" (EDLs) or birth certificates, which might be acceptable for crossing the border by land or sea, are not valid for international air travel. Even children and infants are required to have their own passports when flying. Additionally, if you are a permanent resident of Canada (but not a citizen), you will need your passport from your country of citizenship plus your Canadian Permanent Resident card. Forgetting your passport at the airport will almost certainly result in being denied boarding by the airline, as they are legally obligated to ensure all passengers have the correct documentation before departing for an international destination.