Suggestions by @rockscar

Daniel Cudmore

as Rocket Red in Justice League International

Sonoya Mizuno

as Doctor Light in Justice League International

Peter Dinklage

as Oberon in Justice League International

Katy O'Brian

as Big Barda in Justice League International

Zachary Levi

as Captain Marvel in Justice League International

Camila Mendes

as Fire in Justice League International

Maria Bakalova

as Ice in Justice League International

Zac Efron

as Captain Atom in Justice League International

Brandon Perea

as Mister Miracle in Justice League International

Jason Sudeikis

as Blue Beetle in Justice League International

Glen Powell

as Booster Gold in Justice League International

Nathan Fillion

as Guy Gardner in Justice League International

Maika Monroe

as Black Canary in Justice League International

Sebastian Stan

as Batman in Justice League International

Brian Tyree Henry

as Martian Manhunter in Justice League International

Sean Gunn

as Maxwell Lord in Justice League International

Steven Spielberg

as Director in Superman

Keanu Reeves

as The Billionaire in Superman

Spoiler

as The Billionaire in Superman

Anthony Mackie

as John Henry Irons in Superman