A pally is a plate class.
So they'll be on the upper edge of hit points, for any character - at equal gear level/type of gear.

They do have resistance aura, making them as resistant as anyone is likely to be.
I suppose if you don't have Grounding Totems...
Every class can be two-shotted by mages then.
Although that didn't seem to be the case with my druids, in Cata PvP.