There's always a reason why a pokemon evolves into whatever else, even if it's a bit obscure. The most far-fetched evolution lines would have to be the ones for Charizard, Dewgong, Ampharos, Tyranitar, and Pelipper.
Otter to bear? Not even a connection, besides maybe both of them living in the same hemisphere.
Yeah but it's a very obscure reason in many cases.
Like Octillery to Remoraid is the weapon theme of the two. Wotter has a Samurai theme and while I don't see that concluding at a polar bear, there's no reason to shoot down the idea of it instantly. Gamefreak is pretty insane.
That being said if there was a Water/Fighting Polar Bear and not Ice/Fighting that'd suck hard.