The Hollywood Reporter finally got word on the mystery untitled Marvel property that will go head-to-head with DC's Batman vs Superman May 6th, 2016. It will indeed be Captain America 3! This comes off the announcement yesterday that Marvel is not shying away from battling DC on that date in 2016.
Now there is still the rumor that Batman vs Superman will move up a week but so far nothing official has been made. As it stands Marvel's Captain America 3 will indeed battle DC's Batman vs Superman come May 2016.
This also makes the most sense given if Marvel went with such an obscure character like Dr. Strange, Black Panther or Inhumans, that it would never have made a profit up against Batman or Superman let alone them together!
Marvel still has a second film slated for July 2016 that has yet to be announced...
How confident are Marvel & Disney about Captain America? Apparently CAPTAIN AMERICA 3 will go up against BATMAN/SUPERMAN on 5/6/16. Boom!
— Exhibitor Relations (@ERCboxoffice) March 13, 2014
Captain America 3 hits May 6th, 2016