By Land and Sea (including ferries) - Canadian citizens generally are not required to have a visa or a
passport and may visit the U.S. for up to 6 months. However, Canadians must be able to prove their identity and citizenship to enter the United
States. CBP will accept either a birth certificate, citizenship certificate or
passport as proof of citizenship. If the Canadian citizen does not have any of these because they were lost or stolen, we emphasize that the burden of proof is on the traveler to prove that they are Canadian citizens. Copies of correspondence requesting a replacement of documents, etc. might be accepted, but it is up to the CBP officer to determine whether or not such paperwork meets that burden of proof.
source: US Customs
