不需要 http://www.canadainternational.gc.ca/china-chine/visas/beijing-pekin/visiting-visiter.aspx?lang=eng&view=d United States of America permanent residents [Green Card holders] who are in possession of their status document or who can provide other evidence of permanent residence in the USA do not require a visa to visit Canada. However, if you have been outside of the United States for a considerable period, you must first confirm your permanent resident status before entering Canada.
http://www.canadainternational.gc.ca/china-chine/visas/beijing-pekin/visiting-visiter.aspx?lang=eng&view=d
United States of America permanent residents [Green Card holders] who are in possession of their status document or who can provide other evidence of permanent residence in the USA do not require a visa to visit Canada. However, if you have been outside of the United States for a considerable period, you must first confirm your permanent resident status before entering Canada.