A U.S. traveler driving to Canada is required to carry a US motor vehicle liability card, plus vehicle ownership papers (such as a registration card). A copy of the automobile policy is also recommended to be carried.
The yellow Canadian Non-Resident Inter-provincial Motor Vehicle Liability Card is required as proof that your US auto policy liability limits meet the minimum requirements for each / all Canadian provinces and territories and that your coverage extends to Canada and its territories.
U.S. travelers who do not carry a Canadian Non-Resident Inter-Provincial Motor Vehicle Liability Card and are stopped by Canadian police or are in an accident while driving in Canada risk being fined or having their vehicle impounded until acceptable proof of proper coverage is obtained.
These yellow cards can be obtained from your Insurance Agent or your auto insurance company.