I have brought in 2 cars from US to Canada. I spoke to the US vehicle import office gentleman when I brought over my last car in Dec 2012. (Canadian dollar hasn’t been strong the last few years so no incentive lately in import more) Back then he said that if you didn’t do the 72 hour before requirements & visit their office before taking the car to Canada, when you next travelled back to the US to visit, they can quickly tell with their computers that your vehicle is not compliant and they would fine you $500. Then he added that the fine was going to be increasing to $5,000 in the future. So maybe it has gone to the higher amount by now? Anyways, they didn’t charge a fee to do it properly, so well worth following their rules!