Matt Bomer as Tony Stark/Iron Man-
Reasoning: He's suave, cocky, and has the looks of Tony Stark.
Jensen Ackles as Captain America-
Reasoning: He's proved his comic book movie worth again and again. He's great at playing the dark, brooding, badass that we all deserve to see in a comic book movie. He actually almost got the role, but Chris Evans beat him out in the final round of auditions.
Milla Jovovich as Black Widow-
Reasoning: She can play the awesome gun toting female badass with a troubled past, that's the definition of Black Widow.
Guy Pearce as Bruce Banner/Hulk-
Reasoning: He has played the scientist with a dark side in Iron Man 3, if he were to put a good guy twist on that character we would have one hell of a Hulk.
Ben McKenzie as Hawkeye-
Reasoning: He has been killing it over on Gotham, given the right writers with Hawkeye's humor, Ben would kill it as the archer.
James Marsden as Thor-
Reasoning: This is the most obscure casting decision but I believe James could follow up Thor. He would obviously have to bulk up. But, I see a ton of Thor-like potential in his acting.
Last but not least!
George Clooney as Nick Fury-
Reasoning: I have no preference over which Nick Fury is used, whether he be Caucasian or African American., as long as the performance is compelling! Samuel L. Jackson has been great and I think Clooney can be just as great!