The Regional Transportation District hasn’t even sent out its request for proposals to build its North Metro Rail Project and already has its first unsolicited proposal. The transit agency announced Friday that it had received an unsolicited proposal from Graham Contracting Ltd., a Canadian construction firm that does more than $2 billion in annual revenues. The North Metro project — part of RTD’s sprawling FasTracks transit network — is a proposed 18.4-mile electrified commuter rail line…