I have a friend who is doing the six months thing and last time going back to the US, she was pulled in secondary inspection for two hours. She expects the same thing from now in because the CBP documents everything these days.
Also since the OP mentioned living at a border city, beware the first dead giveaway to the US CBP is your Canadian plate, and the reverse is true if you have a US plated car coming back. Put it simply, they will ask how you can claim PR in one country while living in the other evidenced by where you registered your car. You register your car where you live. So be careful.