I always assumed the system locale was set based on chosen time zone, but that doesn't appear to be the case. I choose Detroit for my time zone (or New York, I've done both), but Ubuntu always sets my locale as en_CA, and points me to a Canadian mirror for apt on a fresh install.
How is locale chosen? How can I make sure my locale is set to en_US? Will that get my apt respositories back to a US mirror?
NOTE: I know how to change my locale, my question is specifically about how to make sure it's set properly on install.