Cavill or no Cavill Superman should be in it. And honestly I trust they can do it without pulling the crap they pull in the TV show where they go out of there way at times to make her look better than him. Infact if they're smart they will take a oage out of WW's book, not once did they belittle Steve Trevor to boost Diana. To me if you do stuff like that you're just showing weakness as a writer. If anyone's read Being Super I would take that as an inspiration but nit an adaptation, have Superman discover her, show a scene or two of him popping in to check on her. Have him come back at the end to give her the old thumbs up.