According to Deadline, a deal has been made that would see Evans in the lead role instead of Franco. I assume that it was a studio decision because we all know Franco would never walk away from a job.
Michael Shannon is set to play Kuklinski, also called The Iceman, and Franco would have played the role of his mentor Robert Pronge. Evans will now be taking that role in the film which is supposed to start production next month.
Evans is known for his role as Captain America in his title movie and the upcoming The Avengers. He also starred in the movie Puncture.