Question: Can I apply for TN status at the border with a passport that expires soon?
Answer: You can go to the border in this situation. Canadian citizens entering the United States at land or sea ports-of-entry do not need to present a valid passport for admission yet. However, for purposes of the TN, you still must establish Canadian citizenship. Instead of a passport, alternative evidence of Canadian citizenship may include a birth certificate and/or Canadian Citizenship Card. If an applicant only possesses a birth certificate, he or she may still be admitted with photo I.D. such as a license.
Also note that at land or sea ports-of-entry even an expired passport is sufficient evidence to establish Canadian citizenship, but an admission stamp will not be placed in an expired passport. A soon to expire passport should not pose a problem for a border TN application. At this point, you only need a valid, unexpired passport when applying for a TN at air ports-of-entry.
Read more about changes to the passport requirements for entering the U.S. by air and by land or sea.