preorder game on my US psn and make it my main or buy it on my main CAN account

i currently have 30$ on my US PSN i could preorder the game i want on my US PSN as im only missing 70 us dollars that would cost me 88$ CAD or preorder the game 129.99 $CAD on my CAD account. The thing is that i gameshare with my brother so if i buy on the us it will have to become my main account..