Canadian nurses moving to US

Hi,
I'm new to the forums...I found this website so helpful when I was preparing to write the NCLEX-RN Now that I've passed it and have my state license I am confused about the rules surrounding Canadian nurses applying for jobs in the US.
I replied to an online job posting on Monster and was invited to an interview. But what do I tell the border service people when I go to the US for this? Is my trip personal or business? Will I get hassled for saying it's an interview? What kind of documentation should I bring with me? I can't get my 212(r) or TN visa until I have a letter offering me a job but it seems that it's illegal for a nurse to actually "look for work" in the US. That's why I've looked online on general job sites but now that it's 'crunch' time I'm totally at a loss for how to proceed.
After working so hard to pass the NCLEX and obtain my US state nursing license I would hate to make a stupid mistake now to mess up my chances of being allowed to work in the US.
Any help or advice would be greatly appreciated!
Thank you,
C61