I'd have to pick Calzaghe on points. He's just way busier, better gas tank and with those freaky reactions. Canelo has much more power and he's no slouch in exploding on a guy either. Ginger's kryptonite is guys that are faster than him, and Calzaghe is MUCH faster let's be honest. I would say that Canelo has his chances because he can uncork face-breaking punches out of nowhere and Calzaghe has been caught before.
Canelo who has stamina issue and likes to fight at his own pace vs a dynamic Southpaw with blazing handspeed and amazing workrate ? Calzaghe runs rings around him and wins a UD.
Calzaghe had the speed and movement and solid chin; IMO Canelo would be the best fighter he faced but JC would be one of the best Canelo has faced. I think Calzaghe wins a close decision at 168