If you just take it across and drop it off, the new owner will not be able to register it... easily or at all. Last time I sold it required me to go through a broker at the truck crossing, not a big deal, but needed my info and the buyers info. I charged the buyer the cost of the paperwork. When I got to the U.S. side, they wanted to see the brokerage stuff, then no problem. The new owner had no difficulty then in doing their paperwork at home. that's my experience
Brian