Well, if he's on a Juggernaut he'll be in a unit of them too - it's the only Monstrous Cav unit in the book, and though there's Tamurkhan Rot Knights they're unlikely and also Nurgle so he can't join them. He'll want a Look Out Sir save from Empire definitely.
So, we'll assume he'll be in a unit of Juggers - and I'm not sure if they'll have a Champ in them, as people tend not to take them due to their having to challenge, which means a lot of wounds wasted in a challenge instead of reducing enemy ranks.
So, it's possible the unit may only have the Lord who can challenge - in which case, due to the wide frontage of the Juggers, the White Cloak idea might still have merit...
Still, be wary of his setup. He WILL have Always Strikes First from a Helm of Many Eyes, and possibly an Ogre or Giantblade - he also doesn't even need a shield with that helmet, so he may even take a Halberd. That's a lot of damage with only 25 points of magic items spent with just the Helm and Halberd.
So, he could have a LOT of other things - Dawnstone (useless admittedly against you), Ward Save, Fire Breath, Poison, Potions... there's a LOT of choice.