In response to an AILA liaison question, the Detroit CBP office provides additional information on its immigrant intent policy with respect to TN visa applications:
AILA Liaison Question: What is the current policy regarding when a non-immigrant is deemed to have immigrant intent? For example a Canadian TN nurse would like to pursue permanent residence. Does the filing of the I-140 or the filing of the I-485 trigger immigrant intent?
CBP Answer: The 485 [i.e., I-485 Adjustment of Status application] definitely triggers immigrant intent. The mere filing of the 140 [i.e., I-140 Immigrant Worker Petition] does not automatically trigger it. If the person is commuting, it is less likely to trigger intent.
However, if they are traveling to FL to work and plan on staying there, a CBP officer is more likely to find immigrant intent.
Any backlogs in processing would be taken into consideration on the particular case.
Once the 485 is filed, the TN must have advance parole to travel.
From Michigan Chapter: Minutes/Q&A of CBP Liaison Meeting, AILA Doc. No. 07111950 (Nov. 1, 2007).