It seems they aren't too sure about John Krasinski.
From Deadline:
EXCLUSIVE: Marvel Studios and director Joe Johnston want to be really sure they’ve found the right actor to star in The First Avenger: Captain America.
Marvel has slightly expanded its search—adding actors that I’m told include Chris Evans, who already logged Marvel Comics superhero time as Johnny Storm/Human Torch in two Fantastic Four films. Of the original contenders, two are still in serious contention: Mike Vogel (Cloverfield) and Garrett Hedlund (Tron: Legacy).
Hedlund was on Marvel’s original wish list but didn't test at first. Scheduling was cited, but I also heard his reps balked when Marvel informed them that the job would include options for 9 future films and a salary around $300,000.
It’s not going to work out for the other actors who tested: Chace Crawford (CW's Gossip Girl), John Krasinski (NBC's The Office), Scott Porter (NBC's Friday Night Lights), Michael Cassidy (CW's Privileged) or Patrick Flueger (Brothers).