Thanks for the reply. I do have a Tern GSD eBike that is similar to what you have used. I had to replace the seat and seatpost to get my butt back far enough to be tolerable at distances over 15 mi./25 km but I have done rides up to 3 times that long since then and feel I could easily do another15-30 mi. if I took a long break in the middle. A couple of these rides included 3-5 miles of 7% gradient which required Level 3 (of 4) assist. Unfortunately at 90#/44 kg, it is too heavy to transport to Europe. (I have used Level 4 assist to get up shorter grades I could barely climb on my old regular touring bike in my prime but that does reduce battery life hugely.) I intend to further explore the limitations of battery life on rides before I go.
However. at ~90 # (44 kg) with empty panniers, it is too heavy to go on a plane even assuming batteries are allowed. So, I will need to rent or buy a bike there to do my tour. I don't need a full touring setup as I expect to avoid camping but I would need to fill a couple medium panniers and a handlebar bag. (Camping would likely make overnight charging impossible in some cases.)
A friend from the UK informs me that he has done some day riding on eBikes in the Swiss Alps and that they are commonly available to rent in many mid-size towns. However, he didn't mention their suitability or availability for longer rides so I will have to research that more. I also don't know what current rental rates are or if there are rental limitations on crossing from Switzerland to France on one.