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, 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.
http://www.cic.gc.ca/english/visit/visas.html