Travel to Canada with a green card is very possible and it is allowed but it depends on the route you are taking, while you can go with your green card through some root others will need you to get other documents or register for an ETA. If you are taking a flight then you need to get an ETA, but for water and land your green card can get you in.
To travel to Canada with a green card, one who is a holder of the United States Green Card does not need to go and get a visitor Visa to travel to Canada unless while flying or transiting through Canada you are required to get an ETA.
The registered eTA is linked electronically to your passport, that is if you have registered, so there is no use printing any document as proof. When traveling through the air, you will be required to bring the following;
- Proof of your status in the United States or your ADIT stamp on your passport that is still valid
- A valid passport that you used when you were applying for your ETA.
When you get to the airport and check in your flight the airline automatically confirms that you have an ETA and a proof of status in the United States. As soon as you arrive in Canada, the officer at the border service will verify your eTA.
If you intend traveling directly from the United States by train, car, boat or bus you will be asked to present only your United States proof of lawful permanent resident status which can be your Green Card or an alien document identification that is valid and telecommunication System stamp (ADIT).
When applying for eTA you enter your ADIT stamp number or the number on your United States lawful permanent resident alien registration card (Green Card)
If there is a case of passport damage or loss that eTA that was registered with that passport is no longer functional, it is advised that you apply for a new eTA when you get a new passport.
If you do not want to go through the stress of applying for an ETA you can choose not to fly, but if you are not patient enough to use a train, car or a boat you should get your ETA.
Read about Green Card Organization