My best guess is that it will be a "friend" of Wilson's, perhaps even Wilson's attorney who is also Wilson's next door "neighbor" AND "best friend". (Remember the FBI in the neighborhood at the last minute).
I'm still trying to figure out why Cooper called Rove on the 11th when it hit the wire but Wilson didn't find out until the 12th when his neighbor (Attorney) waved him over to read the article. Especially since Joe had talked to Novak about the pending article. NO ONE CALLED JOE ON THE 11TH???