The US has announced agreements with both Mexico and Canada to close the border for all but essential travel. Read the Fact Sheet and announcements here. All non-essential travel has been prohibited. We believe this prohibits the issuance of new TN's for Canadians. For Mexican nationals, a new TN requires a visa issued from a US Consulate which are all closed at present. For persons who already are in possession of a TN or other working status, for example, an L visa, it is not clear whether you would be permitted to re-enter the US after a trip to Canada but, we are advising you not to travel unless you are prepared to remain in Canada until the border is opened again.