Travel to Caen from CDG on the GTV train

Any suggestions about what? Also, I think you mean TGV. In any event, to get to Caen from CDG, you will have to go into Paris and catch a train at Gare Saint-Lazare. I am not sure that any TGVs even run on that route but maybe someone with more knowledge will chime in.

Easiest is probably to take Roissybus to Opera, walk 10 minutes to St. Lazare, and take the train from there. You can buy the needed tickets when you are here.

All good advice so far. No TGV to Caen. I am usually alone so I take the RoissyBus from CDG to Gare Saint-Lazare (€13 per person) and the train from there. If I were with two or more or with a lot of luggage, the fixed rate taxi is a good option (€56 for one taxi—up to four people). Both leave right outside of arrivals. Don't take a taxi from anyone inside of the airport.

Please clarify. If I take the Roissybus can I go from CDG to Gare Saint-Lazare or do i go to Opera and then walk to the train station?

The RoissyBus brings you to Opera Garnier—which is a 7-minute walk to Gare Saint-Lazare. Since neither the bus nor a taxi requires a reservation, you can always wait and see what the weather is like when you arrive to make your decision. Both bus and taxi leave right outside of arrivals. The official taxi has footsteps on the floor leading you there and the RoisyBus should have signs above leading you to the correct bus pickup location.

Train service to Caen from Paris is with TER (transport express régional, which locally is called NOMAD) not TGV (train à grande vitesse; i.e. high speed train).

And the train station at CDG is TGV only, so you would need to use transit or taxi to go from CDG to the train station serving Normandie and Caen, with is Gare Saint-Lazare, where you could catch a TER/NOMAD train to Caen.

Not sure what GTV might be.

One small warning: Service on inter-city trains sometimes is limited by track maintenance so it is wise to check the schedule a cautious time in advance.