While the Marvel Cinematic Universe is one of the biggest running movie franchises of today, it has amassed a large cast to play as the plethora of characters from its comic canon. Marvel Studios has never been shy of who they want to play as their characters; from taking risks with upcoming young stars to established actors, to even Academy winners who wouldn't scoff at the amount of money and fame that comes from being an iconic MCU character. While we are sadden by the confirmed news that some of our beloved actors won't be staying in the MCU for long, the start of a new phase in the MCU also means there is be a lot more slots for more actors who could be recruited to put their mark on the MCU.
Originally planned to appear for "Guardians of the Galaxy Vol. 2" before he was only teased at the after-credits, speculations have run rampant as to who James Gunn had in mind to play as the perfect engineered human being. Gunn himself has already dismissed that he would be taking an established but older actor (namely Matthew McConaughey and Tom Cruise being crossed out) but is looking for someone younger. While that means that it is a perfect role for a young actor to make a breakthrough, there should also be a consideration that it needed someone who can handle to pressure of taking on one of the most powerful roles in the Guardians of the Galaxy universe. For that we would like to see Joseph Gordon-Levitt who is not the youngest Gunn could aim for, but he has the fresh look and already far established his acting credentials. His implied connection as Robin or Nightwing in Christopher Nolan's closing installment of the "Dark Knight" trilogy in 2012 is probably the closest to Gordon-Levitt being a superhero, but it would be a fulfilling surprise to see him embody the Soul Gem for an actor who we haven't seen much in recent years since
Another fan favorite from the Guardians of the Galaxy universe but hasn't been hinted to make his MCU debut is Nova. First thought of to be Star Lord's (human) father until that connection is dispelled in Vol. 2, James Gunn has mentioned that he still has future plans for the Nova Centurion (or Marvel's Green Lantern knockoff) to have a part in the MCU (maybe Vol. 3?). Regardless, there hasn't been an announced casting for the character as of yet, so there's still a lookout for an actor who looks good in a helmet. While we would have liked Karl Urban to reprise his helmed persona from "Dredd", but he has already become part of the MCU from "Thor: Ragnarok". So, our next best choice would Armie Hammer. We see that he is able to pull off the dashing and confident saviour archetype as Richard Rider would, like he did in "The Lone Ranger", this might be his next best shot of gaining mainstream admiration (or for redeeming himself for starring in "The Lone Ranger").
Despite constantly being compared to his caped crusading counterpart from the DC Universe, Moon Knight has been one of the fan favourites in the Marvel universe. With the success of Black Panther and given the eventual departure of Tony Stark as the resident flamboyant rich playboy of the MCU, it looks like the time has almost come to look for a new billionaire character for the MCU. While Daredevil might have been the better known broody character from the world of comics, but now that the character has been relegated to small screen performance, there is a chance for Marc Spector to take center stage in the MCU. Moon Knight would be one Marvel character with a more complex disposition than others so far in the franchise. Struggling with multiple personality disorders and fuelled by an origin of vengeance, it would need someone who has a scary gravitas. For that, we couldn't think of anyone better than Jake Gyllenhaal, who has a history of playing mentally dysfunctional characters, heroic or otherwise. Although his past track record of flirting with blockbuster success may make him a little shy (and he has already denied being the next Batman), but we think this is the role that best suits his return to the spotlight, and he already has been envisioned by fans to wear the white cape
With diversity being a major agenda in Disney who owns Marvel Studios, we wouldn't be surprised if Marvel starts digging up more non-Caucasian characters to make their MCU entry. While already set to appear in the "Iron Fist" series, there is still hope of holding out that Marvel Studios are looking to introduce an Asian, if not Chinese, superhero to claim the massive Chinese audience. As to who should play as the Master of Kung Fu and the son of Fu Manchu, Marvel certainly has plenty to pick from a mass of Asian action stars who could swing a nunchaku and is trained in Wushu. If Marvel was going for someone most recognisable in the Asian action market today, it would probably be Donnie Yen, who already has a prior working relationship with Disney for "Rogue One", so it might not seem to be that far-fetched of an idea.
Often compared to another character from DC, but fun fact, Aquaman was actually a response to Namor, so it's only fitting that Namor joins the Avengers, now that Aquaman is part of the Justice League. It would be appropriate to find an actor with a look of mixed parentage to play as the half-Atlantean and half-human, so we don't see anything wrong with Brian Tee's campaign for the role, if the casting call ever comes. However, as for someone who almost looks like Namor and has played a character with dual heritage, it would be Zachary Quinto who has wrestled with issues that comes from his conflicting heritage, and even tested his appearance as the character spotting a similar hair cut as Spock from the rebooted "Star Trek" series.