Advice on Vancouver to El Paso

I’m looking for advice about a possible ride from Vancouver, BC to El Paso, TX in May/June. I need to be in El Paso at the end of June. I’m looking at Adventure Cycling maps (https://www.adventurecycling.org/routes-and-maps/interactive-network-map/) and wondering what route to take.

In broad strokes, I could ride west to Montana on the Northern Tier and then south along the TransAmerica Route to Colorado and then make my own way through New Mexico. I ride a traditional touring setup and am thinking the Great Divide is probably not for me.

Concerns:
– May might be too early to ride the Northern Tier from Washington to Montana

Or I could ride south to California and then ride across Arizona and New Mexico. It seems like my choices are the Pacific Coast route and the Sierra Cascade route.

Concerns:
– Lots of traffic
– Riding on the Pacific Coast Highway sounds dangerous (not much shoulder, lots of summer traffic)

Does anyone have suggestions?

Thanks!