I'm not so sure about this point. So, when we did our soft landing and returning back to the U.S. via Detroit tunnel, the officer asked me if I exported the car and I said not yet, will do a little later in coming weeks. He said he need to check if the car has been exported though he can clearly see it still has U.S. plates. He radio'ed someone and after confirmation that I didn't export, he let us enter the U.S. Not sure what would have happened if I exported the car and tried to bring it back to U.S. without registering in Canada.
So, do more research if you are planning on bringing the car back before registering in Canada.
Agree. Most probably car exported out of USA cannot be driven in USA with US no. plate and insurance.