At long last I found a set of seats in the US (well, actually, I gave up for a while, and then found exactly what I was looking for when I looked again) and had them shipped to a spot near the Canadian border. I hadn't succeeded thus far in finding a set here in Canada.
They had the same set of options - power recline, manual everything else, and heated. Picked them up this week, and all was good with the shipment. No damage, and well packed!
I had no issue deconstructing the shipment and fitting it in the back of the wagon. The two front seats fit like two "L"s and the back seat pieces were no problem as they are all straight and flat.
Yesterday I first took out the passenger seat and looked at the connectors. Oh, no. Two connectors from the seat to the car on the new seats, and three connectors from the seat to the car on the old seats. After further investigation, I saw that luckily the wiring on the seat was all exactly the same, and the connector had been upgraded to reduce the total number of connectors. What this meant was that I needed to carefully undo all connectors on the bottom of each seat and swap the wiring harness from the old seats to the new seats. This made the job longer.
Rather than this taking an hour or so to swap the seats (I guess if you get the same year, this would be the case), it took a couple hours for the first seat, about an hour for the second, and another hour to do the back.
After swapping the harnesses, luckily all worked as hoped, and I now have the GTI Clark Plaid seats in my MK7 TDI Wagon. I also swapped along with the harness, the module on the bottom of the seat for detecting whether there is a passenger in the seat or not. So no airbag light and no module reset via VCDS required (though I do have VCDS, I just figured since the box was attached to the harness I was moving anyway, might as well just take the whole thing).
Much more comfortable for me - I never found the standard seats to be very comfortable for me. After a bit of time sitting I felt like I went completely numb in the rear, as if I'd been sitting on a piece of plywood for a while. Seems like the shape of the GTI seats with the extra bolstering works for me.
So, I wanted to post that since it's the first I'd heard of the wiring harness changing, so that everyone knows, yes, it's possible to use the 2017 MK7 GTI seats but you just need to swap harnesses from the old seats.
Honestly, I think they look great and look better than the stock seats. I don't mind the plaid / tartan look at all.