Casting Gag: In the French dub, Johnny Quick is voiced by Yoann Sover, who is also the voice of Kid Flash/Wally West in Young Justice. In that same dub, the Jester is voiced by Xavier Fagnon, who also voiced many animated incarnations of the Joker ever since Batman: The Brave and the Bold.
Playing Against Type: Looking at their later roles, the idea of Brian Bloom playing a villain and Jonathan Adams playing a hero seems far fetched.
Role Reprisal: 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 Batman: Adrien Antoine as Batman/Bruce Wayne. Averted in the case of Flash. While Christophe Lemoine has voiced several animated incarnations of both Barry Allen (ever since The Batman) and Jay Garrick, this is the first and so far only time where he got to do the voice of Wally West.
From Batman: The Brave and the Bold: In addition to Superman, Batman, and Wonder Woman, Philippe Peythieu as Martian Manhunter/J’onn J’onzz, Michel Vigné as Aquaman, and Barbara Beretta as Black Canary.
From Young Justice: In addition to Superman, Batman, Wonder Woman, Martian Manhunter, Aquaman, and Black Canary, Paul Borne as Lex Luthor.
In the Latin-American Spanish dub, pretty much every actor from the Justice League dub reprised their roles. The closest to an exception was Héctor Indriago instead of Framk Maneiro as Batman, and that's because Indriago began voicing Bruce from The Batman onwards.
The casting of the movie contains two, according to interviews with Bruce Timm. According to one interview, James Wood was set to be in the DCAU version before it got pulled, though it's unclear who he was going to play (Timm said he'd still been Owlman, but Andrea Romano, Dwayne McDuffie and Wood himself believe he was going to play the good Luthor). According to another, Vanessa Marshall, who voiced Wonder Woman for the film, was in the running of the role in Justice League and came close, but the producers picked Susan Eisenberg instead for the series.