Originally Posted by
Asthereal
I responded to this already, but you may have missed it. Kaldheim is legal when it officially launches. So on february 5th, according to the MtG wiki.
About the backbuild: it comes down to the same thing. You always play to win, you just get the reverse score, so the score your opponent would get.
So whether you swap decks and play to win, or you play your own deck and still play to win even tough you don't want to, you get the same result.
The Canadians play just as optimally to win. If they get a better result by playing nothing, they will play nothing. If they get a better result by not attacking, they stay back.