The site also listed that the film was in active development, although it wasn't clear which role Johnson would portray. It would seem likely that he would portray Captain Nemo in the film. Here's the synopsis of the film, as released by the site.
The story begins with the mystery of an underwater "beast" that has been stalking boats, taking bites out of them, and leaving them to sink to the bottom of the sea. Ned, is reluctantly recruited by an old army buddy to hunt the beast. He's joined by Aronnax, a scientist and Julie. They go out looking for this beast and eventually find it. But the beast is not a beast at all...it's a super tricked out mega submarine called "The Nautilus," captained by Nemo, who takes them captive and brings them back to a secret Volcano City. There they learn that Nemo is searching for a lost underwater civilization that holds libraries of vast knowledge and a weapon with the power to destroy mankind. (Studio is fast-tracking the project and hopes to make the film this year.)
We'll be sure to keep you posted on any developments surrounding this film, as soon as we have more information.
What makes Dwayne Johnson right as your leading man?
McG: He's not. I don't know where that came from. I've never spoken to Dwayne Johnson. You can be the first to report that I have no idea where that came from. I wish him every success, but I never spoke to Dwayne about this.
So do you have a leading man, then?
McG: I do not. I'm out to Will Smith.
Well, everyone is running with that Dwayne Johnson story-
McG: I've never spoken to Dwayne Johnson about this. I like him. He's great. He's a wonderful human being and an excellent screen presence, but we have not spoken about 20,000 Leagues Under the Sea. Not a word.