With Ant-man poised to make his debut come 2015 I figured I'd just take a run at this just for fun. So with that being said, let's get to it!
The premise for this film would be to showcase the three Ant-Man characters Hank Pym, Scott Lang, and Eric O'Grady as they're each showed donning the moniker of Ant-Man. The film would then find the three men joining forces to take on a deadly threat that was designed to be self aware, "The Ultron" (A super computer created by Hank Pym), used to monitor the activities of citizens the world over.
Alan Tudyk: Scott Lang/Ant-Man 2
I chose Alan for Scott Lang because the one thing that I get from Alan is that he seems like a very sincere person. This I felt lends him greatly towards the character as I can see him as a family man doing whatever is necessary to provide for his family and afford the best care for his daughter's heart condition. In the film, Lang would be contacted by S.H.I.E.L.D to use his expert knowledge of electronics in order to take down the returning threat of Ultron. Serving time in prison, he gets released for good behavior and is contacted by Fury to undergo treatment with Hank Pym's long abandoned "Pym Particles" experiment to become the new Ant-Man.
Bill Hader: Eric O'Grady/Ant-Man 3
I picked Bill Hader for Eric O'Grady because if there's a guy charming and funny enough to make you care and root for this shameless character it'd be Hader. An imprisoned and disgraced former low-level S.H.I.E.L.D operative, Eric O'Grady escapes and steals Pym's "restored" and newly remodeled suit (Courtesy of Tony Stark due to him looking for motivation for a new suit upgrade a.k.a extremis). O'Grady then sets out to cause as much mischief as he can, as well as spy on the more attractive heroines in the MCU, however he soon sets on a mission to upstage Scott Lang and S.H.I.E.L.D. by saving the day from the Ultron threat. But, the deeper motive would be to make up for the treatment of his fallen partner/friend, Chris McCarthy.
Simon Baker: Henry Pym/Ant-Man 1
I chose Simon out of the countless others mentioned (which wasn't easy to do) because he has this look that I feel would fit Pym greatly for this. He has a look of being disconnected from the world and always being in his head which I feel would fit the character for this story. Many years ago in his younger days, Pym was a brilliant scientific mind who under the influence of S.H.I.E.L.D created a super computer used to monitor and report on the activities of the world populace under it's own control to allow for a set of eyes on things that S.H.I.E.L.D would not always be up to date on. However, upon studying humanity, Ultron found that humans were in fact a very flawed creation. One of our flaws was the lack of evolving or upgrading like our technology, therefore Ultron would create beings that were the best of both worlds: Man and machine made one as he and Hank Pym had become seeing as how Pym programed Ultron's intelligence based on his own. Now connected, Hank Pym became Ant-Man to infiltrate the powerful Ultron computer and shut him down via severing of a shared cognitive link. This leads to Hank becoming a very unbalanced and mentally damaged individual. This event cost him his marriage, his life, reputation, and his sanity. Now, with Ultron returning many years later to finish the job he it started, Hank Pym will come out of retirement/seclusion to put to bed the monster that he himself created.
Morena Baccarin: Janet Van Dyne/The Wasp
A fan favorite, if it's not broke don't fix it. She has the cute and lovable charm required to play Jan to letter.
Benedict Cumberbatch/Ultron (Voice)
Cumberbatch is a natural choice for this role to me because of the steely cold and calculating nature of his portrayal of Kahn in Into the Darkness just sold me on this. Also, the very uneasy and tense presence he brought just with the very sound of his voice.
Cameo Appearances: One of the coolest thing about Marvel films are the easter eggs and the name drops in their films so this shouldn't be any different. A quick shot of the S.H.I.E.L.D containment facility should showcase a few of Ant-Man's rogues ranging from Egghead, Whirlwind, and The Magician. They could actually serve in helping Eric O"Grady escape to further ruin the reputation of Hank Pym. While I don't know specifically who I'd cast, I feel that these actors could play those three characters.
SImon Pegg: Egghead
James Patrick Stuart:Whirlwind
David Tennant: The Magician
I chose those actors because to me Simon has enough charisma and comedic ability to take a character like Egghead and embrace the character in all his weirdness and make him a joy to watch. Pegg just has a presence where you want to constantly watch what he does.
Stuart has much experience with comic book characters doing a lot of voice work. I think it'd be an honor to take a voice actor and allow them the chance to show their faces to the world to get recognition. Also it works great for the Whirlwind character as you get to see the man himself, Then when he becomes the Whirlwind you now have a face to go with the voice.
David Tennant is a bit of bias choice for me because I really want to see him in a comic book movie and I feel with his experience with Dr. Who he lends himself to the science fiction hijinks in the world of not just the MCU but also as one of Ant-Man's villains. Plus, Tennant playing a magician is also an in joke to his role in Harry Potter and the Goblet of Fire.
And this is my Ant-Man fan-cast!