Ali, in his very prime, beats every boxer in the history of the sport. Wladimir, although a great champion, is not an exception.
Ali is not a small boxer, so you can't say he would be overwhelmed by Wlad's size.
Ali has a superior jab.
Ali has a better chin.
Ali is a faster boxer.
He would find the way to beat Wlad. Probably by UD. I can't see him KO Wlad as Wlad is too defensively good to run into punch that would take him out but Ali would outbox him.