This is straight from the Canadian Governments website so I think Im all set
If you are a citizen of the United States, you do not need a passport to enter Canada; however, you should carry proof of your citizenship such as a birth certificate, certificate of citizenship or naturalization or a Certificate of Indian Status, as well as a photo ID. If you are a permanent resident of the United States, you must bring your permanent resident card (i.e. green card) with you.Â