U.S. citizen do not need a visa to enter Canada for tourism or business, and may stay up to 90 days.
CANADIAN ETA VISA
Canada has introduced a new entry requirement, called an Electronic Travel Authorization or (eTA) for visa exempt foreign nationals that fly into Canada. This new eTA will be mandatory effective March 15 2016.
Effective March 15 2016, visa-exempt foreign nationals arriving in or transiting through Canada via air for tourist or business purposes will need an Electronic Travel Authorization (eTA). Requirements for entry by land and sea have not changed. U.S. and Canadian passport holders are exempt from this new policy; however, all other nationalities including those holding a U.S. Permanent Residency (Green Card) (previously accepted in lieu of a visa) must also now apply for and obtain an eTA for Canada in advance of travel.
Nationals of the following 57 countries do not require a visa per se for Canada but are now required to obtain an eTA prior to arrival in Canada by air. All other nationalities still must apply for a traditional visa physically stamped in their passport well in advance of travel.
Andorra, Antigua and Barbuda, Australia, Austria, Bahamas, Barbados, Belgium, British Citizens, British Overseas Citizens, Anguilla, Bermuda, British Virgin Islands, Cayman Islands, Falkland Island, Gibraltar, Montserrat, Pitcairn Island, Saint Helena, Turks and Caicos Islands, Brunei Darussalam, Chile, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Japan, South Korea, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Monaco, Netherlands, New Zealand, Norway, Papua New Guinea, Poland, Portugal, Samoa, San Marino, Singapore, Slovakia, Slovenia, Solomon Islands, Spain, Sweden, Switzerland.
Canadian citizens, including those with dual nationality, are not eligible to apply for an eTA and are strongly encouraged to travel with their valid Canadian passport.