The only Americans I've known to work for Cunard are theater lighting technicans that were recruited through C-deck.com. If you don't know by now, many of the cruise lines 'outsource' the hiring process through hiring partners (didn't you go through one with Celebrity?). C-deck handles the US market for many lines - check them out and see if they can advise you as to why you're having a problem getting in . . . .
(some of their info is kinda dated, and their forums dead, but you might try sending a resume - they've called me twice in the past five years, but I have a specialized skill . . )