i go to canada often times to visit friends, casinos etc. sometimes they ask you to come out of the car and go see INS officers inside, there they check your AP. but if they let you pass without having to get out, then they only check the AP or valid visa etc.
I always felt going into canada everytime is more of a hassle because as a PR of canada, you're suposed to be living in canada. sometimes the canadian officials can be downright nasty.
I don't recommend going back and forth unless it is work related or absolutely necessary. so do as i say not as i do . :>