I wouldn't be surprised if Tua was physically stronger. He was certainly not as fast of hand or or foot, explosive or skilled, but I wouldn't be surprised if he possessed more brute strength than Mike. Wasn't the 5ft 9ins Justine Fortune previously some kind of strong man competitor, or have I got that confused?
Tua maybe as those south islanders are naturally freakishly strong ... I doubt Sharkey or Sullivan as they were much lighter in their primes. Maybe Obie Walker or Sam McVey were more competitive ...
I would take a wild guess that Paul Anderson was stronger. The strongest fighter of any given description, is rarely an elite fighter.