U.S. Customs and Border Protection (USCBP) announced that beginning January 31, 2008, all persons entering the United States from Canada by land or sea will be asked to present citizenship and identity documents. It was announced that oral declaration of U.S. or Canadian citizenship alone would no longer suffice for entry. This is part of the Western Hemisphere Travel Initiative (WHTI). However, despite this announcement, it appears that U.S. land ports of entry along the Canadian border are still exercising some leniency when applying the new transitional rule.
A passport is always acceptable proof without further evidence. Under the announcement, U.S. and Canadian citizens may also use a combination of citizenship and identity documents such as a birth certificate along with a valid driver's licence.
The rules for entry by land and sea are scheduled to become more restrictive as of June 2009.
U.S. and Canadian citizens entering the U.S. by air require either a passport or other WHTI-compliant documents. It is recommended that all Canadian business travellers, whether travelling by air, land or sea into the United States, obtain a passport.