Actually, it is the younger Sub-Zero, you can tell mainly because of the scar on his face, only present in the younger Sub-Zero. And this game has no "timeline" it's non-canon

There is no "timeline". The game is non-canon, so they mixed and matched the versions of the characters they like the best.

Liu Kang is alive and Raiden is in white, but Sub-Zero's scar is blue like it was in Deadly Alliance, Quan Chi has his DA costume with tattoos and amulet, and Sonya and Jax's dogtags say "Outerworld Investigation Agency", which wasn't introduced until after MK3. (plus their arena has a techno-portal, also not invented until post-MK3)

My guess is the Brother. He's the only one who ever had a scar.

Exactly....There are/were 2 Sub-Zero's,MK1 Sub Zero that went Noob Saibot and his younger brother from MK2 till these days.