Katty -

Yes, you could fly into Vancouver.
Alaska Airlines has cheap connecting flights to Portland, Oregon.
And Portland is one of the most bike friendly cities in the U.S.

Here are the two main summer cross-county routes from Adventure Cycling -
http://www.adventurecycling.org/routes/index.cfm

TransAm Route -
http://www.adventurecycling.org/routes/transamerica.cfm
Northern Tier Route -
http://www.adventurecycling.org/routes/northerntier.cfm

The Northern Tier is closer to Vancouver.
You could hop a ferry over to Vancouver Island -
Then take the San Juan Islands ferry to Anacortes - the Northern Tier starting point.
(An inexpensive, gorgeous cruise - maybe camp on one of the islands??)

A word on the Northern Tier -
You have only a short stretch to get your cycling legs before you have many mountain passes to cross.
The TransAm isn't as difficult early on - but the Northern Tier includes Going to the Sun Road.
Going to the Sun in Glacier National Park is the finest cycling in the United States.

After that the Northern Tier gets dicey - a thousand miles of prairie.
But the eastern portions of the Northern Tier are nicer than the TransAm.
Sorry, but Missouri and Kentucky are too hot and have far too many mangy dogs for me.
Or - you could start on the Northern Tier thru Glacier N.P.
Then take US 89 (scenic, low traffic) south to Yellowstone and the Trans Am.

Have you been by crazyguyonabike website?
Here's my stretch of the Northern Tier last fall -
http://www.crazyguyonabike.com/doc/?...c_id=2937&v=Bx

Photo - Going to the Sun Road

Best - J

PS - I have a half dozen cross county trips plus, maybe, 15 extensive tours in the West.
I'd be glad to give you detailed info on just about anything - routes, weather, camping.
I understand that you Brits organiz(s)e things differently, but I'll try.
If you wish - send me an e-mail since I can attach maps etc. more easily - johnegan(at)bresnan(dot)net