Hi, I am having difficulty with getting answers to my questions. I am a Canadian business owner that would like to start provideding my services to American clients. There is an American company who would like to contract me out to their clients to perform third party audits. I will obviously be paid by that US company. My questions are. Do I file a w8-Ben or W-4? I also heard that I need a EIN #? How do I pass customs and what do I need to present to them to have this done all legal?