U.S. green card holders (permanent residents) can travel to Canada without a visa. However, you will need a passport. Canada does not require permanent residents to get a visitor visa. When you travel to Canada, you will need to provide proof of your status in the U.S. (green card) and a valid passport.
美国公民有美国护照进入加拿大无需签证,不明白为什么加拿大转机没戏了? 即使没有签证,不出机场禁区也没问题。