Realistically, whatever kind of cart-broke horse he could find or afford.

Most of the pictures that I've seen show draught horses pulling the wagons, but they could also use Morgans, standardbreds, and various mixed breeds to pull a car.

But, the most common and the most ideal would be a draught breed, like the Clydesdale, the Shire, the Belgian Draught, and the Percheron.