At this point, I really don't think this movie will happen. The film is already presumed cancelled for a tv series instead. But given the fact many still want this to happen, Warner Bros and DC may change their minds, espically since a certain actor wants to portray Black Adam. This is my fan cast should the film actually happen. Some have worked with WB before and some have been in comicbook movies, or played heroes in general. I'll explain my reasoning, because some choices are more obvious then others.
Daniel Cudmore as Captain Marvel
I bet some expected Patrick Warburton or Brandon Molale. Molale isn't the best actor for this, and Warburton is too old for the role. Cudmore is no stranger playing a superhero, after his role as Collossus in X Men, for what screen time he had. Plus, he matches the choice for Black Adam in three ways: they're both good actors, around 6 feet, and neither one work for a big pay check.
Zachary Gordon as Billy Baston
I may get hate for this choice, but hear me out on this. Gordon bears somewhat of a resemblence to Cudmore. I'm aware that Baston is basically a kid who turns into Captain Marvel, but I felt as though the actor who plays Billy should closely resemble Captain Marvel's actor. To add to this, it'll finally let him do something else other then Diary of a Whimpy Kid.
Taylor Dooley as Mary Marvel
There is the common mistake that Mary Marvel is an adult, but she is in fact she's not much older then Baston. I chose Dooley for that reason and the fact she's already played a hero as Lavagirl. Granted, the movie wasn't well recived, but she was one of the best things about in my opinion.
Thomas Dekker as Captain Marvel Jr.
There were two reasons I chose Dekker for this role. One being is that he dose look similar to Jr. The other being he has played a hero before. Watch Terminator: The Sarah Conner Chronicals to see what I'm talking about. Dekker is often casted as a dark character, and given the fact that DC/Warner might go the serious route with this film, he'd be perfect in the role.
Danny Devito as Uncle Marvel
Devito has played a short and stubby comic book character in the past. That role was the Penguin in Batman Returns. Ironically, that was a Warner Bros movie, like the Shazam movie. Now, he's playing a hero as oppose to a villain. Since he's already worked with Warner Bros in the past many times, he probably wouldn't say no to the role.
Greg Cipes as Hoppy the Marvel (voice)
Obviously, Hoppy will be a CGI character. To be honest, Cipes was the only actor I really considered. Why? His voice as Beast Boy on Teen Titans. I figured his voice would work great with this character. On another note, Hoppy may not play a big role, and he may be saved to get his powers for the sequel, if WB/DC decide to do one.
Michael Gambon as Shazam the Wizard
This was a rather obvious choice. Gambon has impressed me with his role as Dumbledore in the Harry Potter friends. The fact that he played a wise old wizard makes him perfect for the role. I know some of you expected the likes of Ian McKellen. I do have him in this cast, but not for this role.
Dwayne Johnson as Black Adam
Do I really need to explain this one? He's the perfect choice for Black Adam. More importatnly, he shows interest in the role. When an actor as big as the Rock shows interest in a comic book movie role, you have to give it to him. Warner would be dumb to cast anyone else.
Dustin Hoffman as Dr. Sivana
Just shave his head and give him glasses and he'll look just like Sivana. He's also around the right age for the role.
Ian McKellen as Tawky Tawny (voice)
This is the role I have McKellen in. He wasen't Shazam the Wizard due to his role as Magneto in the X Men films. I really chose him for his voice more then anything, sinc Tawny needs a calming voice. Tawny has always been a mentor and has watched over Billy for a while and still dose. McKellen's voice in Lord of the Rings fits the description just fine.
Well, that's my Shazam cast. Let's just hope the movie actually happens one day.