回複：請問各位前輩，持TN簽證在美國報稅用哪個表？？

According my 5 year TN experence and my understanding:
1. if you partially work, or your spouse worked or live in Canada last whole year, you should fill the 1040NR and meanwhile fill the Canada TAX return. You may pay some extra tax to Canada due to the tax rate is higher in there. And your 401k still needed to be counted as taxable income in canada tax.
2. If you whole family moved out from Canada completely (including your investment such as house, muture fund and stocks), you can fill the tax as resident, the start date could be the time you move to USA. That way will save more tax.
The above only as reference. The best way is ask profersional tax company.
Good luck!