Travelers from Canada to the United States must provide passport identification upon entering the United States. This requirement was instituted on January 23, 2007, and applies specifically to air travel. This rule applies to both adults and children of any age to ensure that all persons are properly identified.
June 1, 2009, marked the start of new identification requirements from entering the United States by land. The Western Hemisphere Travel Initiative now calls for photo identification and proof of citizenship for people who are at least 16 years old before entering the United States from Canada. Previously, only a spoken statement of citizenship was necessary. Naturally, a passport qualifies as an accepted form of photo identification. However, an enhanced driver's license or trusted traveler card is also sufficient. A birth certificate is acceptable for children under 16 years of age.
The same passport requirements that apply to land travel from Canada to the United States also apply to water travel in terms of small boats and ferry travel. For cruises, the same rules apply on entering a U.S. port. If you remain at sea for the duration of the cruise, document requirements may be different, and checking with the cruise line before travel will help answer any questions.
Failing to present your passport or other required documents upon entry to the United States from Canada will result in detainment. You must verify your identification and citizenship before you are allowed to enter the United States. If you lose your passport or it is stolen during travel, report it to the nearest Canadian or American embassy (depending on your citizenship) as soon as possible. After an investigation, they will issue a replacement passport. Expect the process to take up to a few days.