First, you'll need a Pokemon that can use the 'surf' move. Once you've grabbed one from storage, go to Dendemille Town and then leave via the bridge located in the north part of the town. You'll find yourself in the snowy mountains on a path that leads to the Frost Cavern. To avoid constant battles, feel free to use a Max Repel.
Pass through the cave, heading upstairs through the doorway on the right. Make further progress and you'll eventually find a small stream. Next, use surf to reach the other side of the stream. Follow the path around and head downstairs.
See that big glacier in the middle of the room? Well, that's an ice rock. Run around until your Max Repel wears off, then level-up an Eevee while near to the rock. It'll evolve into Glaceon upon completing a battle.
And Leafeon it´s much easier in route 20 when you first enter it it´s a rock with mossy covers then evolve near it and it evolves.
Source and experience