Which countries citizens do not need visas to travel to the Canada?

USA & GB.

Here's the complete for visa exemptions for Canada:
VISITOR VISA EXEMPTIONS
Many people do not require a visa to visit Canada. These include:

citizens of Andorra, Antigua and Barbuda, Australia, Austria, Bahamas, Barbados, Belgium, Botswana, Brunei, Cyprus, Denmark, Estonia, Finland, France, Germany, Greece, Iceland, Ireland, Israel (National Passport holders only), Italy, Japan, Liechtenstein, Luxembourg, Malta, Mexico, Monaco, Namibia, Netherlands, New Zealand, Norway, Papua New Guinea, Portugal, Republic of Korea, St. Kitts and Nevis, St. Lucia, St. Vincent, San Marino, Singapore, Solomon Islands, Spain, Swaziland, Sweden, Slovenia, Switzerland, United States, and Western Samoa;
persons lawfully admitted to the United States for permanent residence who are in possession of their alien registration card (Green card) or can provide other evidence of permanent residence.
British citizens and British Overseas Citizens who are re-admissible to the United Kingdom;
citizens of British dependent territories who derive their citizenship through birth, descent, registration or naturalization in one of the British dependent territories of Anguilla, Bermuda, British Virgin Islands, Cayman Islands, Falkland Islands, Gibraltar, Montserrat, Pitcairn, St. Helena or the Turks and Caicos Islands;
persons holding a valid and subsisting Special Administrative Region passport issued by the Government of the Hong Kong Special Administrative Region of the People’s Republic of China;
persons holding passports or travel documents issued by the Holy See.

Great Britian. America has to have passport to re-enter America now. So if you go to Canada you must have visa to get back into America.