I "believe" that car dolly licensing is based on your home state registration...in this case it's an extension of the toad. Again, that's my belief...I could be wrong, but have yet to be stopped for a dolly without plates*.
*This includes too many military moves - where the car was towed behind a Uhaul on a rented dolly...Uhaul never had plates on any dollies I ever rented.
Canada and Mexico require plates. And the Acme EZE tow is Canada compliant (something about placards printed in English and French).
We have a 2011 vintage Acme EZE-tow and it has never let us down in over 10,000miles. Have towed everything from a tiny 2 door sub-compact to an E250 15Pax van (dropped the driveshaft).
Be warned...having a dolly can make you the local emergency tow service for friends and family
Congrats and safe travels