http://travel.state.gov/visa/temp/types/types_1274.html#7
Requirements for Canadian Citizens
Canadian citizens usually do not need a visa as a NAFTA Professional, although a visa can be issued to qualified TN visa applicants upon request. A Canadian citizen without a TN visa can apply at a U.S. port of entry. Learn about requirements and more on the U.S. Customs and Border Protection (CBP) website and U.S. Citizenship and Immigration Services (USCIS) website. Canadian citizens can also review information regarding TN visas through U.S. Embassy Ottawa's website.
When Does a Canadian NAFTA Professional Need a Visa? A Canadian residing in another country with a non-Canadian spouse and child would need a visa to enable the spouse and child to be able to apply for a visa to accompany or join the NAFTA Professional, as a TD visa holder. Canadians applying for a visa will follow the same documentation requirements as shown in the sections Mexican Citizens, Applying for a TN Visa, and Required Documentation.
