So the big issue for the JL movie is which Green Lantern should we use. Hal or John. we have the actual first human GL, or the one that adds diversity to the movie and is well known thanks to the Justice League/Unlimited TV series. There is also the issue of the recent Green Lantern movie and them wanting to reboot it. Here's how I would do it:
Now I don't know exactly if this movie takes place with the formation of the league, or if they are already formed, but regardless, I would have the movie use John Stewart.
(Hold On Hold On! What about HAL!!!!!!) I'm getting to that. I would have Hal be a Green Lantern in the movie, but he is not on Earth, and as Hal is an older and more respected lantern, Hal deal with more of the major GL issues such as universal doom and major GL threats, while John is mostly centered on Earth and deals with Earth threats. This provides a good explanation as to why Earth has 2 Green Lanterns as Hal is not just some regular Lantern and deals with the bigger issues.
If the league is forming in this movie, I would have there be passing references to this with maybe the flash says something like, "I thought the Green Lantern was white" or "What happened to the other guy" and John would reply with "He's moved on to bigger and better things" implying all I've said above.
This solves so many issues. diversity somewhat, The Hal vs. John issue,with them both sort-of in the movie. Also using John Stewart as a second GL takes care of rebooting Hal Jordan with a new actor or new personality, as that movie could practically remain in continuity with JL taking place years later. This could also lead way for the actual GL movie to do what the Iron man movies did where they had it central around John Stewart and as movie 1 is an earth threat and Hal Jordan is only a background character offering advice and debating with the guardian for Johns favor. But in the much higher stakes second movie, They team up to take down some major universal threat, like in Iron man with War Machine.