Canada: Remember that going to Canada from the United States means crossing an international border

All travelers now need a passport or other accepted secure documents to enter or reenter the United States. Naturalized U.S. residents should carry their naturalization certificate. Permanent residents who aren’t citizens should carry their Permanent Resident Card, more commonly known as a green card. U.S. residents entering Canada from a third country must have a valid passport, naturalization certificate, or green card.