Well since the movie is supposed to be Scott it is a good bet he will be ant-man in A.A. Pym may make an appearance as creator of the shrinking formula. It puzzles me why Pym and Wasp have been cut out of the Avengers movie universe. They could have skipped the bits that probably scared them away from using the characters. Janet doesn't have to be the flake flirty dummy she was in the 60s. Sue Richards and Jane Foster are not portrayed that way in the movies and girl characters were not Marvels strong suit in the beginning. Pym being damaged by the growth process might even make a good sub-plot without adding the abuse stigma-though it would be interesting to see Jan become infuriated and blast him into the hospital instead of just allowing it to happen. Plus Giant-Man and Wasp would make great visuals.
The real question is will Ant-Man be a regular on Avengers Assemble or just a guest character. I'm hoping he becomes the eighth official member of the team. After all, there should be more members for Season 2, same way they added more characters in Justice League as episodes progressed.