Multiple Pokémon received new forms and evolutions in Pokémon Legends: Arceus, but that doesn’t mean Game Freak skipped out on bringing at least a few of the originals into the new game.
You will end up seeing a lot of Hisuian Sneasel and its evolved form Sneasler as the latter is one of the Pokémon that helps you traverse the varied landscapes of the Hisui region. You won’t be running into any Johtonian Sneasel in the wild unless you go out of your way to find them, though.
This is because that form of Sneasel isn’t native to Hisui and can only be encountered in a space-time distortion, a type of event that takes place on the map that can spawn rare items and exclusive Pokémon you won’t find anywhere else.
For Johtonian Sneasel, you will only be able to encounter it in space-time distortions you enter when traveling in the Obsidian Fieldlands. You can also find Weavile, but that is a much rarer encounter.
If you don’t manage to find a Weavile, you can simply use a Razor Claw on your Johtonian Sneasel at night to trigger its evolution.