Why not take the "Balmoral" (Fred. Olsen) Singapore/ Vancouver sector of its 2009 world cruise see something of Alaska, disembark at Vancouver, see the Rockies and cross Canada by rail from Calgary. There are sailings from the US and Canada to bring you home. Good luck and happy travellin.
Gosh I envy you - what a fantastic trip. If I were you and had your £££s I would visit a traditional Travel Agent and ask them to put together a package that involved two transatlantic sailings (Cunard of course) and two train journeys one across the States and other across the Rockies (see www.GreatRail.com). It might involve a few nights of stop offs but what the hell. Enjoy.