Earlier quoted context omitted.
I am not a lawyer. The transition from TN->GC is possible too under the right (narrow) circumstances. The big tradeoff is not risking travel while within the lifecycle of one TN term, and likely not being able to straddle a GC application across the boundaries of a TN renewal period at all. For some countries of birth, a TN term is not long enough to get through the GC pipeline. But for Canadians born in Canada, ones…
It's totally possible to go from TN to GC but you won't be able to leave the United States from the point you file your I140/I485 until your Advanced Parole document turns up. You also can't get a new TN should you need one.
How long does this take usually?