Suggestions by @vincentwilliamsiii

Lightning Lad

as Garth Ranzz in Superman I

Brainiac (Vril Dox)

as Vril Dox/Collector of Worlds in Superman I

General Sam Lane

as General Sam Lane in Superman I

Glen/Glenda Ray

as Glen Glenmorgan in Superman I

DeSaad

as DeSaad in Justice League I

Steppenwolf

as Steppenwolf in Justice League I

Starro

as Starro the Conqueror in Justice League I

Ice Cube

as Silas Stone in Justice League I

O'Shea Jackson Jr.

as Vic Stone in Justice League I

Denzel Washington

as Silas Stone in Justice League I

John David Washington

as Vic Stone in Justice League I

Lucas Till

as Barry Allen in Justice League I

Lucas Till (The Flash)

as Barry Allen in Flash II

Flash (Lucas Till)

as Barry Allen in Flash II

Lucas Till

as Barry Allen in Flash II

Chris Pine

as Eobard Thawne in Flash II

Lucas Till

as Barry Allen in Flash I

Sam Worthington

as Orin in Aquaman I

Joel Edgerton

as Atlan in Aquaman I

Jada Pinkett Smith

as Lucia in Aquaman I