Leafeon can just use work up to boost both attacking stats. This might allow it to get past steels since it can now use hidden power fire with decent power behind it despite the base 60 special attack. It's already really fast, too, so it's possible for you to just invest in its attacking stats and save a little bit for speed in case sun is canceled out.
Something like this. The speed EVs allow it to outspeed max speed Deoxys-S, probably the fastest thing you'll encounter in OU. The rest was poured into attack and then special attack. It's possible to modify it to suit your needs.
Leafeon (M) @ Life Orb/Leftovers
Trait: Chlorophyll
EVs: 252 Atk / 144 SAtk / 112 Spd
Naughty Nature (+Atk, -SDef)
- Hidden Power [Fire]
- Work Up
- Leaf Blade
- Return/Baton Pass