For the cornbread: In a large bowl, add the cornbread and toss with the Cheddar Jack, mozzarella, parsley and scallions. Season with salt and pepper.
For the dressing: In a large pan, add the bacon and cook until crisp. Remove, leaving the fat behind, and chop. Add the chopped bacon to the bowl of cornbread. Add the sage, celery, onions and garlic to the pan and saute until everything is tender, 8 to 10 minutes. Add everything, including the fat from the pan, to the cornbread and toss.
For the liquid: In a separate large bowl or liquid measuring cup, whisk together the melted butter, buttermilk, stock and Worcestershire sauce. Season with a pinch of salt and a few grinds of pepper. Slowly mix into the cornbread until the mixture is moist enough to spread but not wet enough to drip--you may not use all the liquid. Taste and season again with salt and pepper if needed.
Preheat the oven to 350 degrees F. Coat the bottom and sides of a 9-by-13-inch baking dish with cooking spray.
Add the dressing to the prepared baking dish, gently pressing down to even the top. Cover with aluminum foil and bake for 45 minutes. Uncover, raise the oven temperature to 400 degrees F, and bake until the top is golden brown, 10 to 15 minutes more. Serve warm.