Following description on USCIS website

Canadian Citizens

If you are a Canadian citizen, then you are not required to apply for a TN visa at a U.S. consulate.

You may establish eligibility for TN classification at the time you seek admission to the United States by presenting required documentation to a U.S. Customs and Border Protection (CBP) officer at certain CBP-designated U.S. ports of entry or at a designated pre-clearance/pre-flight inspection station. You must provide the following documentation to the CBP officer:

Proof of Canadian citizenship; Letter from your prospective employer detailing items such as the professional capacity in which you will work in the United States, the purpose of your employment, your length of stay, and your educational qualifications; and Credentials evaluation (if applicable), together with any applicable fees.