For sponsorship question, TN can answer no.imo, "No".
"Sponsorship" implies some kind of financial guarantee or obligation to file paperwork.
A TN permit doesn't require the employer to be even aware you are applying for a TN (although it helps a lot). Let alone pay lawyers, file paperwork, or pay fees. (Unless they choose to for some reason).
In practical terms, employers care about 'sponsorship' for 3 reasons:
1. Costs
2. Quotas
3. Processing delays
None of those apply to TN applications done at the border.