I've toured in the US, and in the summer of 2016 did about 500Km over eight days between Bretagne and Normandie as part of a longer tour. One wild camp, seven nights camp grounds. I was refused water in one small village by an old farmer, but that man's son was very apologetic and gave me some.

I found France to be like the US in most of the ways you asked about.

It was a hot and sunny period in July of 2016 when I was in France and I saw men working outside without shirts on, they were all sunburned. If they tried that in our Southwest they would have been incinerated.

In the Southwest, just to be safe I think you should anticipate up to about 140Km between available water and plan accordingly.

After decades of use I now avoid any sort of sun lotion or sun block, I find a broad-brimmed hat and long sleeved-shirts and pants to be far more effective. This is how I rode from Texas to New York in July of 2014, full sun most of the way and I never even began to get burned.