Frazier/Tyson can go only 2 ways whether you like it or not. Tyson early (1-6) or Frazier late (7-12 or 15 depending on what era you go by). It won't go the distance. Tyson's advantages: speed, power, defense, chin, jab, boxing skills... plus he's naturally bigger & stronger. Frazier's advantages: stamina, endurance, heart, inside fighting, left-hook (if that means anything). From assessing their styles, strengths & weaknesses - I pick Tyson by KO/TKO in 5, with Frazier having his moments, but not having enough to keep Iron Mike off him.
You are right that it can only go 2 ways, but in both instances Mike wins. Either he KOs Frazier fast or he wins it on points since he's the more skilled boxer.