This reply by Oceanic is rather interesting. Reminds me of a case a few years ago when a young guy won a photgraphic course in Seattle, quit is BC job, packed his trunk with photographic equipment and proceeded to the border. Flat refusal for entry. One, he should never have quit his job, they told him he had no substantial ties to Canada. He didn't in their eyes, sure his family lived here, but he was single and free. So they were right. And secondly, you just don't arrive at the US border and tell them what you are going to do in their country work wise, or student wise, you need paper work and approvals in advance.
The real problem is that so many people cross that border to shop or vacation and never think of anything else, never have a problem and so never get a rejection. Everyone gets lulled into a sense that everyone else will get across with very little effort. So just say the wrong thing and bang you're out. Right now.
I stood in line behind a young guy at the YVR airport who told the border guard that he was going to San Francisco. He volunteered that his friend was having computer problems and had paid for his ticket to go and help. He was immediately rejected because he was being compensated by some one in the US for entering the country.
So no, it is not a sure thing. Keep your mouth shut, answer only those questions asked, no volunteer information, and make sure you have no secondary business items or illegal items for their country, on you.