France has a lot of cross country lines which are often far better served than is claimed.
Starting from Caen you would catch a TER to Le Mans. From there you can continue on either to Tours or to Nantes via Angers.
From Nantes down the West Coast line to Nantes, then on to Bordeaux.
So far we have avoided the in and out of Paris. From Bordeaux you may go through Paris, but there are direct TGV's to Champagne-Ardennes TGV for local trains in the region. To find those mess around with SNCF Connect, and generally find the Cross Country services mentioned above. Today I see one at 0854 arrive 1255 for instance.
So the whole of this can fairly easily be done without once touching Paris again, if you don't want to.
From the Champagne country I would go to Strasbourg, switch trains to Basel, switch trains for Lucerne- total journey time 4 hours to 4:30.
This is one instance of a map- https://about-france.com/france-rail-map-hi-res.htm