Thanks Jamawani & Cyclebum!
Our endpoints are not fixed as we intend to start and finish in new places. Neither of us are Southerners or Westerners actually, I'm from Minnesota and my partner is from Brooklyn, where we both currently live.
The NorCal/SFO to the Western Express to southern Utah/southern Colorado - Then either cutting down via the Grand Canyon option sounds pretty appealing. As for the end point, if we do West to East, we would like to finish somewhere South Carolina, Georgia, or Florida.