Yes there is the train RER B between Paris and CDG T1 and T2 (we often see some cabin crew using this service)
there is a bus service RATP between CDG and Opera
There are the air france coaches (les cars Air France) between CDG and Champs Elysees - Etoile
It can take more than an hour by bus or car due to dense traffic jam, rain, etc..
I think you can find more accurate information on the ADP website.
Good luck and vive la République, et vive la France!