Any suggestions on which sites to purchase through? I'm really only seeing Rail Europe. Thanks everyone.
Use the French site. http://en.voyages-sncf.com. Change trains and stations in Paris. Uncheck the "direct trains only" box and use France as ticket collection country.
It's worth checking the German rail site as well (www.bahn.de) and seeing which offers the cheaper price. It shouldn't make much difference in terms of what trains you see.
You cannot book tickets on the German Rail site for rides entire outside Germany. However, that site has the best detailed timetables for the entire route, including Caen-Paris.
What is your travel date? If you book ASAP (up to 90 days), you can get discount fares. The cheapest tickets sell out fast.
Depending upon your departure time, you may have to change trains in Mannheim. If so, you'll save money by booking Paris-Stuttgart on the German Rail site because the second leg is entirely outside France and the French Rail site will charge you full fare for it.