All the dealer has to do is sign a Affidavit of Non-Use. This takes the car out of the California system. You then don't have to pay any title transfer or any of the other taxes that California wants when you buy a car there (and there is a bunch of them).
You get your own insurance from your own insurance provider and a temp registration from the province you live in. Pay the dealer, get your bill of sale and the signed title from them and take the California licence plates off the car. Stick your temp registration (issued from the province where you live) in the window and drive off home.
California Department of Motor Vehicles