Foreman UD Old George's jab alone would keep Tua away for the most part. He wouldn't be able to bully Foreman on the inside or take him out with one big left either.
Foreman's jab pounds him into submission. I mean, really pounds the fight out of him. Tua would shell himself, ala against Lewis. You want to stop Tua? Get a jab going. Ask Rahman --- as mediocre a fighter as the world-stage has ever seen. Foreman's jab runs Tua ragged for a fairly wide decision. 8-3-1, Foreman. Just a different class of boxer.
Foreman easy. Foreman still had his jab even in his last fight and a jab is all you need to beat Tua. He's just too big for him especially the fat Tua. Foreman would jab away and win a boring UD.