What movies would have been better with alternative actors in the lead role?

Actors turn down roles for a variety of reasons. Often iconic lead roles are not the directors prefered choice. Yet most of the actors who play these parts are so renowned for doing so we can’t see anyone else but them playing the role. However just for fun, what movies that you enjoy do you believe would be better served if you could change the actors involved & who would be their replacements? Eg. Would Paul Newman & Steve Mcqueen in say Cool Hand Luke/The Great Escape, have suited each others roles just as well?