Places to consider between London and Strasbourg. We will have already been in Belgium and not planning on Paris for this trip. We will be traveling by train.
One issue you need to be aware of is that the default (fastest) travel option by rail between London and Strasbourg has only one stop, for a change of trains (and stations) in Paris. It's from Paris Nord Eurostar to Paris Est, about 1/2 mile, so walkable if you have wheeled luggage.
You'll probably want to select your stopover(s) carefully so that you don't have to take regional trains the entire way from Paris to Strasbourg, which can take from 7-1/2 to 11 hours.
I liked Nancy very much and I see that Epernay of Champagne fame is also on the slow-train route. I haven't been to Epernay. I don't even recognize the names of most of the other intermediate stops.
Where can I find more info on the slow train route and it's stops??
the DB website is easiest. https://www.bahn.com/en/view/index.shtml. After you get initial results click on show details then click on show intermediate stops.
That's the website I used, entering Paris as the starting point, un-checking the "Prefer fast connections" box, and checking the "Local transport only" box.
I would suggest instead to go straight on to Strasbourg and spend your time in the Alsace. There are lots of little villages to explore and they have well-signed wine and cheese routes to take throughout the region. My favorite town is Colmar but some of my other suggestions would be Riquewihr, Kayserburg, Ribeauville, Epinal and Obernai. There will be wineries in and around all these towns that do tours and tastings. Some other places of interest in the area - To the southwest of Strasbourg near Natzwiller is the only Nazi-constructed French concentration camp. It is the Vosges mountain, an interesting stop and a beautiful drive in the mountains to get there. Down below Colmar is an open air museum, the Ecomusee with old houses and buildings brought from around the region and reconstructed here. It would be very easy to spend a day here. There are also several castles ruins in the area. Haut Koenigsbourg is intact and well worth a visit. It's between Strasbourg and Colmar. If you want to duck into Switzerland, Basel is about 45 minutes from Colmar and just over the border. You also have the option of crossing over the Rhine into the Black Forest. Freiberg is about 30 minutes across the river from Colmar. There are a number of spa towns like Bad Krozingen in the Black Forest if you want to have a day of pampering. The Alsace is a great region to explore for a number of reason so I would head straight for Strasbourg.