Itinerary B. Why spend the extra 2-3 hours backtracking to CDG and back (or limiting yourself to Antwerp departures from CDG)? In mid-January everything will be less crowded than during vacation time so you probably won't have to queue at Gare du Nord for as long as you think (though I haven't done it so can't speak from direct experience).

By the way, Sunday shopping even on the Champs-Elysees might be more limited than you imagine.

ETA: thinking about it, I suspect the more important question is whether you can indeed do the shopping you anticipate on a Sunday. The Champs-Elysees does have more things open on Sunday for tourists, but not everything.