Generally the breed doesn't business, as long as they can be trained to pull or behave well in parade/many relatives ceremonies and that they are the right color- black or white/gray.
Generally breed doesn't matter, but black coloring is necessary
Answers: They used to use Fresian horses for the most part for the military caissons. Now they use different breeds mostly thoroughbred mixes, draft mixes, and Percherons. For example, the riderless horse in Reagan's funeral was a standardbred.