Joshua will knock him out mid to late rounds . I truly believe that he could finish him early , but I don't reckon he is going to take any risks of a big shot connecting. So I reckon AJ will keep him at the end of his jab and force Miller to take chances. It'll also sap Miller's energy trying to get inside and wear him down.
I don't see the fight being any fun to watch, and I don't see Miller throwing caution to the wind despite all his big talk. People will say Joshua didn't look good , just because he's being patient, but in reality, it'll Miller that embarrasses himself as despite his bravado , he'll go down with a whimper.