Marseille is way, way off the direct route from Bordeaux to Barcelona.
Shoshana, it sounds like you plan to pick up a car in Paris and drop it in Barcelona. Doing something like that usually results in a very high drop charge--many hundreds of euros. Although good train routings between Bordeaux and Barcelona are infrequent, there are departures at 10:34 AM (6 hours) and 12:34 PM (7 hours) that require just one change, in Narbonne.
The central part of this itinerary seems like it has a lot of driving. You'll be driving around the Loire Valley, then you have a significant drive to Bordeaux (time required depends on where you start from, obviously), so it will probably be mid-afternoon by the time you get to Bordeaux (you'll need breakfast and lunch). After less than 1-1/2 days in Bordeaux, you're facing a 6-hour drive to Barcelona, which will put you in that city fairly late, giving you not much more than three sightseeing days in a city which could certainly use more time than that. I look forward to seeing Bordeaux on my next trip to France, but I don't think I'd be willing to do all the driving you plan in order to include it in this itinerary, and I'd certainly rather have that time in Barcelona.
I'm quoting ViaMichelin time-estimates above, which are thought to be a bit optimistic and which definitely do not include any stops, looking for parking, getting lost, etc. Traffic impact around both Bordeaux and Barcelona could be an issue as well.