Local or International admission

Your best answer will come from your Canadian consulate or the US State Department rather than here since 99% of the members are high school kids answering these posts.

Your son is Canadian and piggybacking off your TN Visa so from what I've read he will have to convert his dependency status to his own F1 or M1 Visa prior to matriculating in an American college. The only way he would be able to apply as a non-international student to my understanding is if he was born in the United States or has DACA status.

There might be some local provisions for children of TN Visa to apply as in-state residents because your family has lived in NC for 3 years but you would have to check with NC schools directly like Duke, NC State, UNC, Wake Forest, etc to see how they would treat your son's admissions and whether you would benefit from in-state tuition.

I would think that the other 49 US States would consider him out of state at best and most like an International applicant.

Consulate General of Canada – Atlanta

1175 Peachtree Street

100 Colony Square Suite 1700

Atlanta, GA 30361-6205

Telephone Number: (404) 532-2000

Email address: atnta@international.gc.ca

Territory: Georgia, Alabama, Mississippi, North Carolina, South Carolina, Tennessee

https://educationusa.state.gov/foreign-institutions-and-governments/understanding-us-higher-education/international-student

Good luck