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. Because a permanent resident is not eligible for a U.S. passport, you will need a valid passport from your country of citizenship.
Flying vs. Driving, Required Travel Documents to Enter Canada
If you are flying to or traveling through Canada, you will also need an Electronic Travel Authorization (eTA). To apply for an eTA, you need a valid passport, a credit card, a debit card and an email address. The cost is $7 CAD and you can apply online; eTAs are valid for 5 years.
If you are driving to Canada or traveling by bus, train or boat, you do not need at eTA. However, you must carry your green card.
What If I Don’t Have a Passport?
According to the Canadian government website, you need a passport to apply for an eTA and to enter the country in general. However, the news website USA Today, along with other online sources such as the travel website Travelocity, report that it is possible to travel to Canada with only a green card.
Whatever you decided, know that the Canadian government has the right to refuse you entry into the country.