SnakeDoctor
Super Freak
Though Superman and Batman are so well known with a total between them of 13 films that there s no need to reintroduce them for JL beforehand.
I think they need to reintroduce them ... but not necessarily an origin story. As far as I'm concerned, Batman Begins is the definitive Batman origin ... no need for another. I'm open to a redone Superman origin because its been 25 years since the last one, and a lot's changed.
Either way, I don't think it'd be as good for the first appearance of an actor as Superman or Batman to be in a JL movie. Those two are big enough that they need their own franchise, and deserve their own universe separate from the Justice League ... and it works better if you establish that universe for that actor before establishing the JL. Starting them in a JL movie, and then spinning them off into their own franchise shortchanges them too much. They have to preexist the Justice League.
I'm fine with Nolan's Dark Knight Trilogy and Snyder's Man of Steel being lead-ins though.
SnakeDoc