Characters should look like the characters they represent. An 'in shape' actor isn't enough for Cap. He needs to be BIG. He needs to be blond and he needs blue eyes. He has to be a decent actor, not necessarily a great actor.
The movie should be set during WWII where he is fighting Nazis. Start off like the comic where he is fighting saboteurs on the homefront, then in Europe since Nazis seem to be the only ones the PC police allow you to call evil. Maybe we can teach some of the younger generation what the greatest generation knew, namely recognizing evil for what it is, not cultural diversity.
The movie should end with him going into suspended animation to set up film number two. Cap is (yes is, because we know he WILL be back) a living legend and he needs to be portrayed as such and more importantly, WHY he is a living legend, namely his leadership and inspiration during the war.