This is just my opinion on who should play them in a reboot of a JLA film.
Now, onto the cast:-
Batman/Bruce Wayne-Bradley Cooper
Superman/Clark Kent-Chris Evans
Flash/Barry Allen-Armie Hammer
Wonder Woman/Diana Prince-Jamie Alexander
Green Lantern/Hal Jordan-Chris Pine
Martian Manhunter/John Jones-Idris Elba
Aquaman/Arthur Curry-Liam McIntyre
Plastic Man/Patrick O'Brien-Jim Carrey
Red Tornado/John Smith-Christian Bale
Joker-Tom Hiddelston
Harley Quinn-Rachel McAdams
Lex Luthor-Patrick Stewart
Otis-Adam Sandler
Alfred Pennyworth-Jeremy Irons
Damian Wayne-Jake T. Austin
Kilowog-Vin Diesel
Mera-Catherine Zeta-Jones
Hippolyta-Megan Fox