Sgt. York will be the rider less horse during the funeral procession.
I saw a special about his selection and training on Animal Planet. He was offered as a good candidate, and they weren't sure about him because of his small size.
It occured to me that it would be extra special if he were to carry Reagan's own saddle and boots. Not sure if that will be done here, but I do think it would be extremely cool if he did.
Notice the farrier in the background. Probably putting borium shoes or studs on his shoes so he won't slip on the pavement.