hjf said:
This is getting technically scary! So the odds is 50/50?
Here's my opinion.
If you get denied TN status at the land POE, then you are already technically in the US, and you do not show him your H1b visa, then he will most certainly admit you in B2 status, in which case this would void your H1b, since you cannot be in 2 statuses at once.
If after your TN is denied, and you show your H1b, then you may be admitted in H1b status. The problem here is since you have to actually pick which status you want to enter in, and you picked TN, and it was denied, the officer may not let you retrack that unless you exited the US and reentered and claimed H1b status, at which point it would have already been cancelled. Consult with a lawyer.
The tricky part is if you went to the PFI in a Canadian airport, and your TN was denied. If you did not proceed to get on a US bound flight, and you also did not show your H1b, then its hard to tell what the officer would have done with your previous H1b status. He could have voided it upon reviewing the TN application, or he could have left it alone. You'll never really know.
On the other hand, I'm not 100% postive, but I think when I was denied TN status at the land POE the first time around, I was admitted into the US in an "Out of Status" status, and the officer essentially warned me that if I proceed past the U-turn to get back to the Canadian border, I would have violated US immigration law, and this was a serious federal offense, jail, barring for 10 years, yadda yadda, etc. etc.. If this were true, then I was not admitted in B2 status as I assumed, so maybe (had I had H1b) it would not have voided my H1b status.
Thus the answer is.....maybe....just as TheRealCanadian stated above.