Moving car through U.S. from Canada on temporary registration?

Hello,

I'll be buying a car in another province in Canada and driving it
back through the U.S. to my home province with a temporary registration
permit. This means that the car will not have any plates in place and
will only have a temporary paper permit placed on the front window.

To me, this seems somewhat risky to drive long distances, through two
countries with no plates.

Am I more likely to get stopped or hassled at the border in this
situation?

Has anyone done this before and have you had any problems?

Dave