You can technically apply for a green card but border guards can and do use it as evidence that you don’t intend to stay “temporarily” and deny your TN as a res

You can technically apply for a green card but border guards can and do use it as evidence that you don’t intend to stay “temporarily” and deny your TN as a result. They can reevaluate your TN status at every crossing, and there are many stories of this happening to people returning from holiday when I was at microsoft. The TN is efficient to get but has its downsides.