If you are travelling before the December timetable change, there is also the option of the Nice to Paris Austerlitz InterCité Nuit overnight couchette train, which calls at the main stations to Marseille-Blancard (note that it doesn't call at the main station in Marseille (St. Charles) as it is a terminus!)
This service takes bikes for the standard €10 SNCF bike carriage fee, although you do have to travel in the couchette portion and not the seating portion, as the connecting doors between the two parts of the train are kept locked for security reasons!
Sadly, this train will not run after December, as passengers now prefer to use the TGV, or low cost airlines. The portion which runs to Briançon will, I understand, continue to run, as the TGV is not an option - there's not many 300km long 1500V DC extension cables!!
I used the Briançon service in June, and it is a very pleasant way to travel, as long as you avoid Friday and Sunday evening services, which is when most of France seems to travel!
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