Hello! stephaniemajor99,
Thank you for your question! It is my understanding that the taxation of the RRSP will depend on whether or not your son is a qualified beneficiary, at least in regards to Canadian inheritance laws (US accountant here). Assuming he receives the assets in the RRSP, he will not have any US inheritance tax to pay but there could be some state inheritance taxes. He may also be taxed on the earnings of the RRSP.
I have an article here that has some good information. https://turbotax.intuit.ca/tips/what-happens-to-your-rrsp-when-you-die-15766#:~:text=So%20the%20full....
