I could see Keanu Reeves would make a great Mandarin.
I don't want to see Mark Wahlberg. The logical choice for Captain America is the Winter Soldier. There isn't any replacing Chris Evans. It's that simple. Keanu would have been perfect for Iron Man. He's the right build. However, he's a unique actor. He chooses his movies carefully.
On another note; if someone should be sought out for a new Indiana Jones, it should be Joe Flannagan, from Stargate Atlantis. He's perfect for the role.