U.S. citizens must present passports in order to enter Canada by all means, according to TripAdvisor. In March 2016, an additional entry requirement called the eTA will be a requirement for travelers who enter Canada by air. Travelers must complete the eTA online before travelling to Canada, according to the Canadian Government.
The documents required to cross the border between Canada and the U.S. depend on the traveler's citizenship and his method of travel. Because of changes in U.S. law that took place in June 2009, U.S. citizens must now present valid U.S. passports in order to cross the Canadian border and can no longer present just driver's licenses and birth certificates, notes USA Today. They can then stay in Canada for six months, beginning on the day they enter.
A traveler completing the online application for the eTA to gain access to Canada will have to pay CA$7 to receive it. This entry requirement only applies to foreign nationals from countries that are visa-exempt and who travel to Canada by air, with an exception of U.S. citizens and travellers with a valid visa. For land and sea entry, travelers only need valid passports, according to the Government of Canada.