TGV accessible seat with dog
I would disassemble the kennel by separating the top and bottom pieces and stacking them inside each other and just take it with you into the train car. It will be much easier to carry this way, also takes up a lot less space. Disassembled, it should fit in the luggage area. Also, you'll be able to pass the turnstiles @ CDG with a disassembled crate and will not need to wait for staff to open the handicapped gate, which can take a very long time and lead to you missing your train, which is what happened to me once.
Assuming you'll be on a Thalys train, the best seats with a dog plus crate are the accessible seats in coach 1/11 ('premium comfort', first class). Definitely go with First Class. I always reserve seat 23 and put the dog next to me. See seat map here:
https://www.thalys.com/sites/thalys....o_Rames_EN.pdf
Unfortunately, SNCF suspended their '
mes bagages' baggage check-in and delivery service last year, so checking it and having it delivered isn't an option currently. It should eventually reopen, so check the website every now and then for details.
edit: Here's a picture showing how much space there is:
