I saw another article like this and felt like I wanted to put out my own fan casting. I agree with a lot of @MicahJamesNebeker fan casting and even surprised me with a well casted Tigra. So here is my own:
Sean Bean as Taskmaster
Give Sean Bean a sword and what does he do with it? He becomes an ultimate badass actor. He has a good rep and can pull off the look quite well.
Zac Efron as Iron Fist
Zac has a weird history. Despite being a good actor and a good guy, some people still don't like him. The thing is, Iron Fist could be pulled off with some comedy and Zac has the look and acting skills for it. He also has the young age that we want to see.
Scott Porter as Sentry
If you have seen him in Music and Lyrics. You would realize that with just longer hair, he is Sentry. He has a not so action-like rep but he is a good actor.
Mary Elizabeth Winstead as Spider-Woman
There's something about Mary. She does the most random roles and is a fairly well-rounded actress, to complete the circle, she should play a superhero.
Rachel Nichols as Captain Marvel
Have you seen her with blonde hair? Stunner. She is quite the action chick and would be a good pick for Captain Marvel.
Tom Cruise as Captain Mahr-Vehl
Now this is interesting. Tom Cruise is short. Kree are tall. He can give a good alien performance and I think he has quite the look, despite the height.
Jensen Ackles as Nova
Four words. Jensen Ackles as Nova. Hell yeah, this is perfect for any day. If only he didn't love Supernatural so much....
Sam Claflin as Speedball/Penance
Penance is an interesting character. Sam is an interesting character. He has a good look to play Speedball and when Speedball goes all Penance, he can give the performance we would want to see.
Karl Urban or Matt LeBlac as Wonder Man
To be honest, both of these guys would be perfect. Karl is a good actor and so is Matt. Matt played Joey who was a wannabe actor and Wonder Man is also one. Karl would give the more badass side of him.
Jared Padelicki as Adam Warlock
It doesn't take much acting skill to be Adam. Just have the look and Jared definetly does. And plus, we could have another joke episode of Supernatural where Sam and Dean maybe meet a guy named Adam Richard who is a very powerful guy and it would just be.... amazing.
Blake Lively as Angela
First of all, she looks like a female Chris Hemsworth. Angela is Thor's long lost sister. She is also knowledgeable when it comes to superheroes as she was in Green Lantern.
Josh Brolin as The Punisher
Despite being Thanos. He could still play a character that shows his real face. Josh Brolin is also scary enough to be The Punisher, he also has the hair.
Casey Affleck as Moon Knight
I have always seen Casey as crazy looking. Marc Spector is clearly insane. And he also is used to heist movies and could play a good Moon Knight using a heist-ish take on him.
Thomas Brodie Sangster as Cannonball
Honestly, have you seen The Maze Runner? He is perfect for a character like this. Also, he would fit the powerset and would totally fit in an X-Force movie.