At one point, the story was going to feature an entirely original superhero named Cobalt, a woman abducted by aliens in the Forties and returned years later with superpowers in order to help fight off the Centre.
The story was meant to originally end more introspectively. Superman would've been revealed to be recovering on some island with Aquaman as his only friend there, and the two would discuss the pros and cons of humanity. Darwyn Cooke opted to remove this because it was too low-key...and gay.
In the French dubnote which was done MANY years after the movie was made, unlike the majority of the DC Universe Original Animated Movies, several voice actors from other adaptations reprised their roles here:
From the DC Animated Universe: Emmanuel Jacomy as Superman/Clark Kent and Véronique Augereau as Lois Lane.
From The Batman: Adrien Antoine as Batman/Bruce Wayne, Alexis Tomassian as Robin/Dick Grayson, and Christophe Lemoine as the Flash/Barry Allen.
From Batman: The Brave and the Bold: In addition to Superman, Batman, Wonder Woman, the Flash, Lois, and Robin, Philippe Peythieu as Martian Manhunter/J’onn J’onzz, Michel Vigné as Aquaman and Captain Cold, and Nicolas Marié as Dr. Magnus.
From Young Justice: In addition to Superman, Batman, Wonder Woman, the Flash, Martian Manhunter, Aquaman, and Captain Cold, Vincent Ropion as Ray Palmer, and Michel Vigné as King Faraday.