In any case, travel time by train from either CDG or Paris-Nord to Brussels is only 1h20. Then again, if Brussels is just a brief stop on the way to the mystery destination, it does take a certain amount of time to get to Zaventem from the city.

If you miss your connection at CDG, take the train to Brussels, sleep there (after a beer at the Grand Place) and be on time for your next flight.
Brussel Centraal to airport is 18 minutes by direct train.