It'll be hard to actually do these EVs since it's still mid game. Volt Switch doesn't exist in Gen IV. Getting the exact nature is going to be difficult since Eevee eggs take forever to hatch. Overall not the best answer. I would still suggest Jolteon however because Barry's/ whatever you named you rival's Floatzel has Ice Fang. Even with that, Leafeon still has high defense so anyone you choose will be fine.