My money goes on Walker.
His early 616 persona is exactly the kind of jingoistic, ultra right wing type character they would need for the role, a little mentally unhinged, cocky, arrogant but undoubtedly patriotic in his own way.
His initially aggressive, showy, strutting, media-savvy approach to dealing with problems (hiring the buckies to make himself look good/taking down villains on live TV/publically challenging Steve Rogers and decrying him as a 'has been' etc) is a good analogy of a war in which body counts, soundbytes and spectacular news footage of Americas so-called irresistable and unbeatable technological might in action were often valued more than the traditional path to victory of taking land from the enemy and then holding it.
Dont forget also that when Walker was first introduced the Vietnam War wasnt that long ago and much of his desire to represent his country came from the fact that his brother Mike had been KIA in Vietnam. He and his attitude were very much products of the Vietnam era.
I would say he's tailor made for the role, although modern 616 Walker is a very different hero.