Sonny Liston footwork combined with his punching ability. Vitali Klitschko never back down and iron chin. Liston by KO in mid rounds.
Vitali has an even worse inside game than wlad. Atleast wlad accepts his limitations and clinches, vitali ridiculously tries to fight his way out of the inside. If anyone can back him up it's sonny. Once sonny starts banging and vitali bangs with him, vitali will find himself being tore a new arsehole. Liston by mid round stoppage.
Sonny was Mentally Fragile and would fold he wouldn't be able to get to Vitali and would crumble after eating a bazillion jabs. I don't see any way Sonny could win this unless by a cuts stoppage.