How can a Canadian open up a business in the US?

One possibility, if you have access to sufficient assets, would be to seek an E-1 (treaty trader) or E-2 (treaty investor) visa - Canadians are eligible for both visas. The first option allows the individual the opportunity to conduct business between the home country and the US, and the second option would allow the individual to start and run a business - in a managerial capacity - where he or she had invested a sufficient amount of money.

As the previous answer stated, your best bet is an E-2 visa.

E-2 is probably your best bet. Be careful as to the amount of investment. It cannot be a small amount. You will have problems if the investment amount is not proper in the eye of the officer for the business that you will be opening.