According to BigShinyRobot.com, their reliable source in the Paramount/Marvel confirmed that the studio is indeed only considering unknowns/television actors to portray Captain America on the big screen.
"Apparently, when the script came in with World War II sequences (featuring the Invaders), the studio heads decided it was beyond their means to make this movie AND afford A-listers like Brad Pitt and Matt Damon."
The source, who remains unnamed, specifically pointed out Chad Michael Murray (One Tree Hill), Ryan McPartlin (Chuck) and Jensen Ackles (Supernatural) as being among the top choices.
We've already heard from other sites that both Murray and McPartlin have potentially read for the role, but this is the first (albeit unofficial) word that fan-favorite Jensen Ackles is in serious consideration.
It looks like we'll have to wait until March 1st to find out solid news regarding this casting. Until then let's follow an age-old CBM tradition and put it to a vote!