By avoiding Eurostar (Red, ex-Thalys). Via Lille with TGV InOui and Kortrijk or Tournai to Brussels (via regional trains, TER & IC).

When are you travelling? Is it just Paris-Brussels and back, or is it part of a longer journey on the day you’re travelling?

Im travelling on 22 Of  Dec.  Paris-Brussels 

I might go to bruges and ghent in the middle of the day

Thanks 

Then you will be surely better of by taking the TGV to Lille, where you can change for a direct local train to Kortrijk/Courtrai and Ghent. Change in Courtrai/Kortrijk for Bruges.

Plenty of TGV’s between Paris and Lille, best reserve one quickly. As it’s probably going to be a busy day, with lots of people heading to their family for Christmas. Reservation should be 10 EUR (sometimes 20 EUR per person). You can buy your reservation e.g. here: https://travel.b-europe.com/Eurail-GE/en/booking-tgv#TravelWish

The local train towards Kortrijk & Ghent departs every hour at hh:09, usually from Platform 15 in Lille Flandres. No reservation needed.