SNCF from Paris to Bordeaux Returning Bordeaux to Colmar

Having never scheduled a round trip on SNCF, I would advise booking two separate trips. For the Paris-Bordeaux trip, for the TGV, book as early as possible for the best price, as the lower prices sell out fast. That is just over 2 hours from Gare Montparnasse.
It looks like Bordeaux to Colmar requires two changes for the shortest trip (just over 7 hours) or one change for an almost 9 hour trip.

Book both trips through SNCF, not a third party site.

I would book a one-way Paris-Bordeaux then another one way Bordeaux-Strasbourg (there is a direct train that runs twice a day from Bordeaux to Strasbourg with no need to change trains or go through Paris. You will need to change trains in Strasbourg to Colmar. I would book all of this on the SNCF app.

. . ."(there is a direct train that runs twice a day from Bordeaux to Strasbourg with no need to change trains or go through Paris. . . "

I am still seeing that I have to go through Paris, though, for a trip of @ 5 hours.

I am still seeing that I have to go through Paris,

There is a daily direct train (between 8am and 9am) from Bordeaux to Strasbourg which does not go through Paris, it goes via the south of Paris.

I should have mentioned that we will be driving our rental car back to Bordeaux from Sarlat-la-Caneda and then taking the train. I'll look again to see if there is another direct connection later than 8-9 a.m. which would be too early for us.

I don't think there are any other direct trains to Strasbourg later in the day. It's not a common route (I mean bypassing Paris). One train a day that's enough to handle the average number of daily passengers, adding another train wouldn't be profitable for SNCF.

But you should check the SNCF Connect website, it can vary depending on the day of the year, especially if it's a busy holiday.

https://www.sncf-connect.com/en-en

If you can't get to Bordeaux station in time for that train, you'll have to take one first train to Paris and another to Strasbourg/Colmar.

It does seem that way JoLui. A long day of travel in France or a day less in the Dordogne and a night in Paris, carrying on the next day to Colmar appear to be our choices. All in all, not bad. No complaints from me while in France.
Thanks to everyone for your suggestions.

Just in case, other options, but not by train:

Flights to Strasbourg from Toulouse or Bordeaux. The airline Volotea offers daily service on both routes.
Driving from Sarlat to Toulouse-Blagnac Airport is easier and faster than going to Bordeaux Airport, as traffic around Bordeaux is very heavy, whereas going to Toulouse-Blagnac avoids driving into Toulouse itself.

I assume you'll have a rental car, which is essential for visiting the Dordogne. You'll find all the major rental companies at the airports to return the car.

Check the Volotea flight schedules.

https://www.volotea.com/en/

Note that this is a low-cost airline, the base prices shown do not include baggage. Don't be fooled by the "Megavolotea" offer, which isn't worth it. Choose the Standard Fare and add checked baggage if necessary.

Many thanks everyone. We have decided to break up what would have been a long travel day and spend the night in Paris. The next day we'll take the train to Colmar and spend three nights. Merci!

Paris is ALWAYS a great idea, even for one night!