Based on this cover art, rumours of this DVD being an adaptation of the second Superman/Batman storyarc are confirmed. Also confirmed is that Green Arrow will be the star of this round's DC Showcase.
Tim Daily and Kevin Conroy will reprise their roles as Superman and Batman from the first entry in the Superman/Batman franchise, Public Enemies.
According to TVGuide.com, added to the voice cast is Summer Glau (Firefly, Terminator: Sarah Conner Chronicles) who will be playing Supergirl!
The article notes that Glau will be the fifth Firefly cast member to be part of a Bruce Timm production. Here are the others: