True, the United States and Canada do not require visas for citizens of both nations to make nonbusiness visits to one another. Once tourist visitors to Canada only occasionally had to produce a driver's license, but it is now becoming a practical requirement to carry a passport. Canadians buying a business in or expanding one to the United States face a mass of regulations. The same goes for expansions from south to north. Information about how to send a manager from one jurisdiction to the other, in either direction, is the subject of whole chapters of books published by immigration experts, usually lawyers.
Some regulations particularly chafe.
Lest you think I am blaming the line INS officers, I am not. You have to remember they are only carrying out the laws and rules set down by Congress and their senior agency staff. An overly open mouth may mean trouble. Another law on the books of the United States has been suspended for 30 months. Known as Section 110, it requires each and every Canadian entering the United States to check into the country with the INS and then check out again.