stadacone30 wrote:My question is, do I qualify for the TN status, knowing that I will keep being paid in Canada and not by the US client? This American client is not an affiliate company or a subsidiary of my Canadian employer, just a regular client.
There's actually two problems here, the second one is tax. I think it is possible to go in as TN-1, because you can be sub-contracted by a US employer to another under TN-1, this is more complex though, it would need to say "so and so of such and such company acting on behalf of company x" instead of just "so and so" in the job offer letter. This is one of the cases where I think running it past a decent immigration consultant is probably a good idea.
Software developer is also not a TN-1 category. I know some people get in to do it under Systems Analyst but the FAM specifically warns CBP against letting in programmers in this category.
Your Canadian employer needs a US payroll to pay you in the US though. Which requires them to have an EIN etc. so they can give you a W-2 and you would have to file a 1040NR and 8840 and claim a foreign tax credit next year.
If there was some way they could directly employ you for five months this would all be much more simple. The job offer letter would be far easier and the US employer could issue the W-2. I realize this exposes your current employer's markup to them but from a legal standpoint it's far simpler.
Steve.