How to set Postgresql database to see date as "MDY" permanently

How can I set my database to see the 'date' as "MDY" without running: SET datestyle = "ISO, MDY"; every-time I'm trying to access it? I'm using Postgresql version 9.1, Ubuntu 12.04. My system locale, at the time of the database installation was set to en_CA.utf8 and I recently changed it to en_US.utf8. show lc_CTYPE returns: --> "en_CA.UTF-8" but show LC_CoLLATE returns: --> "en_CA.UTF-8"