I grew up in Vancouver, a stone's throw from the border, so I suppose I take it for granted that we all learn very early on that CBP is a wretched hive of scum and villainy, and everyone knows someone who was chewed out, berated, and generally treated like a criminal by them.
Seeing as how I work in the US now, it's probably fortunate that I grew up with such a cynical view about crossing international borders.
Anyways, let this be a lesson to Canadians (or I suppose more generally, all non-Americans) who want to cross the border for whatever reason: be prepared always for the worst. If you are crossing for business, always seek legal advice for your situation, and make sure all of your ducks are lined up in a row. You have no right to enter a country where you are not a citizen, regardless of what treaties and protocols your two nations have set up.
I do have a question for the author though: what kind of training involves setting up a US corp? Also, regardless of how you classify it in your head, I'm fairly certain that setting up and working for a US corp, for profit or education or just plain fun, means you're working in the USA, and would be illegal without the relevant visas.
Without knowing the specifics about his situation, it would seem to me that he was in fact trying to enter the US illegally - though he didn't seem to know this. Ignorance of the law won't help you very much when you're in a room with an irate CBP officer.