http://traveltips.usatoday.com/documents-needed-between-canada-usa-car-21162.htmlWestern Hemisphere Travel Initiative
According to the Western Hemisphere Travel Initiative (WHTI), all persons entering or re-entering the U.S. from Canada by car must have a passport or one of the following WHTI compliant documents. These documents include things such as the Trusted Traveler’s Cards such as Nexus; state-issued enhanced driver’s licenses, Enhanced Tribal Orders, U.S. military ID with travel orders, U.S. Merchant Mariner Document when traveling on official maritime business, Native American Tribal Photo ID card or Form I-872 American Indian Card.
Canadian Border Crossing Laws
Canadian law requires all persons entering Canada from the U.S. by car present proof of citizenship and identity. A passport fulfills both of these requirements for U.S. citizens. It is also possible for a U.S. citizen to use their Nexus card to fulfill both of these requirements. In lieu of a passport or Nexus card, a U.S. citizen must provide a government-issued photo ID such as a driver’s license and proof of U.S. citizenship such as a birth certificate or naturalization certificate. However, be warned that if you go to Canada by car with your driver’s license and birth certificate but no passport you will not be able to re-enter the U.S. with these documents. Make sure that anytime you travel out of the U.S., to obtain a passport unless you have a Trusted Traveler’s Card such as Nexus or other WHTI -approved documents.
Citizens of other countries traveling between the U.S. and Canada by car need proof of citizenship from their country and proof of identity. A passport from his country or a WHTI-compliant document will satisfy the border requirements for both the U.S. and Canada.
Pay close attention to at the US border rules relating to reentering the US. It's much easier to enter and drive through Canada than it is to enter the US. If you leave the US to travel through Canada and then reenter the US in Alaska, it's a this crossing where you better have the right documents. These rules apply to traveling on land. There are different rules fro traveling by air.
