Is it better to fly to Paris and take the train or fly to brusells and take the train when your destination is Lille, France?
There is frequent direct TGV service from CDG to Lille Europe. The trip takes about an hour. You won't even have to go into Paris.
To see the timetables go to www.bahn.de. Enter Aeroport Paris-Charles de Gaulle TGV as your departure station and Lille as your arrival station.
When you arrive at CDG find the Tourist Information Office to ask about your trip. They can answer your questions. Ask how to find the RR or bus station in the terminal. Avoid going into Paris.
I've taken the TGV train Tim recommends. Much more convenient to get to Lille from CDG airport than from Brusells. I purchased a discounted ticket online and picked it up at the SCNF office at the airport. It was all very easy.