Since there doesn't seem to be any heavyweight boxer on the face of the earth that can take the physical punishment Mike Tyson dishes out, I propose a matchup with someone who can take the hits. Andre the Giant. If Andre manages to sit on Tyson before Tyson can knock him out, Andre wins.
Who else have we got left? George Foreman? Remember, Michael Spinks made about $145,000 a second for losing. At least Andre could go five rounds.