Between Paris and Strasbourg probably somewhere in Champagne country would be best ... Reims is right on the motorway ... or Epernay might be another option .. it's a smaller place and is just off the motorway
Between Strasbourg and Munich ... The Black Forest is lovely , but wouldn't really break the journey (it's very close to Strasbourg and it a bit out of the way from the main motorway route you'd take to Munich) .. Tubingen or Ulm might be better choices