After 2 winter grand trips one kayak, one raft and a third planed for Jan.
Buy a dry suite! Get the best one you can afford. Make sure it has a piss zipper.
Or create a non dry suit training schedule for the month before the trip:
Wake up take a cold shower, after which put on a cold wet cotton shirt. Then maybe a pre frozen wool sweater pre cooled in the freezer. Repeat this process at to ensure your body is shivering from cold 12-18 hours a day. Do this for 25-35 days.
If your having fun the entire time you will not need a dry suit on the grand in december.
On that note: Do not forget your calories from fat. 1/2 stick of butter a day will give you 500 calories. A tea soon in your tea, breakfast, and lunch will get you there fast and your body will love it.
If you choose the non dry suit rout I would consider 5 sticks of butter a day.
See sec 11/ 2:16 of the film below: