There aren't many regional variants this generation but tomorrow will confirm one of these.

First off, all of Eevee's evolutions will receive regional variants, but not Eevee itself.

The method for evolving Eevee has changed, now, all evolutions require maximum friendship until being able to be evolved using stones.
Vaporeon - Water Stone
Jolteon - Thunder Stone
Flareon - Fire Stone
Espeon - Sun Stone
Umbreon - Moon Stone
Leafeon - Leaf Stone
Glaceon - Ice Stone
Sylveon - Shiny Stone

Eevees evolved in Scarlet and Violet will become regional variants

Vaporeon - Water/Dragon
Jolteon - Electric/Fighting
Flareon - Fire/Poison
Espeon - Psychic/Rock
Umbreon - Dark/Ground
Leafeon - Grass/Ghost
Glaceon - Ice/Steel
Sylveon - Fairy/Flying

Eevee also receives a new evolution using the Dawn Stone - Eeveeon. Which is Normal type. Unsure whether this evolution is a regional evolution or just a brand new one.

Zubat and Golbat receive new regional variants and become pure Flying type. Golbat evolves into a new Pokémon.

Spinarak and Ariados become Bug/Dark

Mantine receives a new Water/Poison regional form. It's evolution from Mantyke requires it to be in the party as a new fish Pokémon.

Combee and Vespiquen become Bug/Grass. Male Combee receives a new evolution.

Skorupi becomes Bug/Fire and receives a new evolution that remains Bug/Fire.

Eelektrik and Eelektross (but not Tynamo) receive new Electric/Dark forms.

Bouffalant becomes Normal/Fighting

Gumshoos becomes Normal/Ground, said to be the original form of Gumshoos and that Alola's Gumshoos is in fact the regional variant.