If you have a car full of brand new luxury goods going into the US, customs and border patrol are absolutely going to pull you in for further inspection and questioning, and they will make you pay the tariffs. They were incredibly shitty to me every time I crossed as part of my job a decade ago, I can only imagine now.
Also if/when they catch you, you're now on American soil and dealing with their legal system, they're not going to just turn you around and let you go back into Canada.