The perfect actress everyone wants for Wonder Woman doesn't exist. You can find plenty of guys who can emulate the big, beefcake body that superheroes have in the comics, but the reality is that in real life, women having bodies like Diana does in the comics is not universally appealing. So you can cast a big buff female bodybuilder or fitness model and have a lot of more casual fans think she looks like a freak, on top of likely being a bad actress, or you can cast a good actress who is probably too short and will look silly coming up to Superman's shoulder no matter how fit you get them to look. The tall, buff but not too buff, great actress doesn't exist in Hollywood. At some point you are going to have to make concessions.