Big Frank Bruno was a match for any HW for 6 rounds Just like Earnie Shavers. His big problem was stamina. Frank in his prime would KO Wilder in 4
Wilder has a punchers chance, but against a big hitter like Bruno he'd fight a cautious fight like he did against Stiverne and Arreola and so he'll take away his best chance to land a big shot due to his caution. Of course if it goes late he could stop Bruno as big Frank tires. But Bruno's heavy jab would give Wilder issues. Wilder has been defending and struggling with guys Bruno would blow away other than Duhaupas who is durable enough to perhaps lose a decision to Bruno. Molina and Szpilka would be quick KO's for Bruno. So I say Bruno softens Wilder up with the jab then KO's him.
It depends on what version. 1989 Bruno walks through Wilder. 1996 Bruno loses by decision or late stoppage.