If Johnson declares he will run then I don’t see anyone beating him. Sunak commands the centre ground one nation tories, with few exceptions Johnson commands the rest (Brexiteers, Red and blue walls). Once it goes to the membership it will be Johnson by a country mile. My guess is if Johnson does declare he will stand uncontested.
Forming a competent cabinet will be a challenge and he has the investigation hanging over him. The best bet would be for him to not run, then come back after tories get defeated next election as the great saviour but these are nothing if not crazy times.