Well I'll start out by listing the actors who were casted already to play the parts.
1. Henry Cavil as Superman
2. Ben Affleck as Batman
3. Gal Gadot as Wonder Woman
4. Jason Momoa as Aquaman (Maybe)
5. Ray Fisher as Cyborg.
Now I will fan cast for the rest of the league and who i want to be in the league.
6. Idris Elba as Green Lantern, John Stewart
I Think Idris Elba would be the best choice for John Stewart, he obviously looks the part and he is a very good actor. I know he plays Heimdall in the Thor francise but i feel they are wasting his talent for a minor part.
7. Michael Rosenbaum as Flash.
I believe Michael Rosenbaum would make a great Barry Allen, hes a decent actor and he is also very funny. He also voiced the flash in several diffent animated seriers, and animated movies.
8. Emily Blunt as Hawkgirl
I always though Emily Blunt should play in a Comic Book Movie, and i think she would make a fantastic Hawkgirl. She's a great actress and is very attractive. Every movie i seen her in i enjoyed and thought she was great. She was great in Edge of Tomorrow, Five year engagement, The adjustment bureau and many more.
And thats my fan cast, let me know what you guys think.