Passports and Visas
Citizens of the United States need a passport to reenter the United States from Canada. Passport requirements apply to minors as well. Anyone under 18 traveling alone should carry a signed and dated letter from both parents or from all legal guardians authorizing the trip. It's also a good idea to include a copy of the child's birth certificate, custody documents if applicable, and death certificates of one or both parents, if applicable. Citizens of the United States, United Kingdom, Australia, and New Zealand do not need visas to enter Canada for a period of six months or less.
Before your trip, make two copies of your passport's data page (one for someone at home and another for you to carry separately). Or scan the page and email it to someone at home and/or yourself.
If you're renewing a passport, you can do so by mail. Forms are available at passport-acceptance facilities and online.