Wow, exciting trip! We are next door in Alberta, have done quite a bit of travelling in the NW of USA where we always had a good time. Friendly people. Our tent trailer was perfect for the climate. Except when venturing into hot country. At Yellowstone we poured pails of water over each other.
Our visit to Disneyland and Joshua Tree park was by airplane and rental car. Also very nice but I was shocked at the heat in the desert. We could only stand being away from air conditioning for half an hour at a time - in November. The coast was great - we even had the beach near Disneyland pretty well all to ourselves because it was too cold for the locals, just right for us.
Cell phone - call your Canadian provider and ask about a month of roving in the US. Usually very reasonable. Be aware of its data limits and keep an eye on your phone's usage. Or turn off the cellular data and just use wifi when available.
