From 2 July 2017 the new faster TGV highspeed train line to Bordeaux (TGV Atlantique) will open bringing Bordeaux to just over 2 hours from Paris compared to over 3 hours previously. The new line will also reduce times from Paris to destinations in Brittany, the western Loire Valley and the south-west such as Toulouse in just over 4 hours saving over an hour on the previous journey time.
There will however be a slight increase in fares on the new line which has been built to compete with the budget airlines. However, as the timings are from city centre to city centre and with less onerous security screenings/check-in times this looks to be a most attractive option. Fares will range between €32 and €55 depending on the time of day.
For more info see TGV