Cubchoo is just a small bear with a cold. Both its English and Japanese names give the same idea.
Small bear with a cold
If anything, Beartic is the tsundere Pokemon.
It's Japanese name is Tsunbear (ツンベアー, tsu-n-be-a~), combinations of tsun-dere and bear?
I thought it was obvious. Maybe that's just me.
Seriously though, it's just Gamefreak either running out of ideas or wanting more bear Pokemon. Just because two Pokemon look similar doesn't mean they're based on each other.