The Canadian Border Services Agency (CBSA) requires adults to supply proof of citizenship and proof of identity to enter Canada. Children under 16 need only prove American citizenship. A valid passport or passport card suffices to prove both citizenship and identity. Passport cards are good for entry only by sea or land, but not sufficient for air travel.
If you don't have a current passport, you'll need a government-issued photo ID, such as a U.S. driver's license, along with proof of American citizenship: an American birth certificate- original or certified copy--original certificate of naturalization, or an expired U.S. passport.
Frequent border crossers can use their passports to sign up for a WHTI-compliant document, the NEXUS card, an expedited border crossing program.
The documentation requirements for adults reentering the U.S. by land or sea are the same as for entering Canada. But it is important to note that if you return to the U.S. by air, adults absolutely must present a valid U.S. passport; other WHTI-compliant documents will not suffice.
Minors under 16 years old can reenter the U.S. by air, land or sea with just a birth certificate, Consular Report of Birth Abroad, or certificate of naturalization. If traveling with a school, religious or other youth group, the age restriction rises to 19.
The NEXUS trusted traveler program expedites the American-Canadian border crossing process for pre-approved, low-risk, frequent frequent border crossers. If you are approved, the cost is $50 dollars (American or Canadian) for a card that is valid for 5 years, as of 2010. With the Nexus card, you can use designated lanes at land crossings and call-ahead service at sea border crossings.
If traveling with a minor who is not your own, the CBSA may require a notarized affadavit from the minor's parents giving consent in order to enter Canada. You will also run into trouble entering Canada if you have a criminal record, including misdemeanors or DWIs; a special waiver coordinated well in advance of travel may be required.
