The main reasons this would happen is even though you are a us citizen then internet ip address you have is based in Canada and that is what Myspace would read to put you in a domain country
You have an IP address that is identified by the Myspace PHP script as Canadian. Basically there is a php function which can take the IP address of the client computer. After this an IF/THEN statement is formulated to connect the client to the correct country server in the myspace network.
It may be that while registering into myspace you must have used the canadian extention like wise as yahoo! There are many extentions of yahoo like. com for United States,. co. in for India,. co. au for Australia.
This could possibly be due to spyware/adware in your system. Download the latest version of Spybot SD and Adaware SE and scan your system for spyware. Or this could possibly be due to a problem in your connection.