No, but from my previous post, “When a Canadian resident rents a U.S. car in the U.S. and drives into Canada, he/she must obtain a Traveler’s Vehicle Permit from Canadian Customs, Form E50B. Then the renter must go directly to a Canadian Hertz location and exchange the U.S. car for a Canadian car within 24 hours.”
So it’s not entirely prohibited, but you need permission and better get rid of the thing quickly.
I wonder if it’s the same thing backwards? When the minivan I was driving broke down in Ontario, I rented a Suburban with Canadian plates from Hertz. No mention about not taking it into the 'States. Border guard didn’t even seem to notice. It was several days before I took it back. Actually the Canadian immigration guy was the bigger questioner: you’re American? Why the Ontario plate? Herz? Do you work for them? And so on.