Yeah, no 48 hours. When I did it I trailered it. The car I bought was actually built in Canada, and this was post-nafta, so no duty :). I did however have to pay the sales tax at US customs. No big deal, I was going to have to pay it when I registered the car anyway. And I got lucky and the newbie at customs was the the suck at math and I ended up paying about half what I should have for sales tax.
But I certainly wouldn’t try the borrowed plates things. If you do hopefully the man with the rubber glove will be gentle.