Heat a large saute pan over medium heat and add 1 tablespoon olive oil. Add the pancetta to the hot oil and render its fat. Once it begins to brown, add the ground pork and prosciutto and cook, while stirring, about 4 minutes. When the pork is no longer pink, add the garlic and sage and saute until fragrant, about 1 minute more. Deglaze the pan with 1/4 cup white wine, scraping up the browned bits from the bottom of the pan. Stir in the bread crumbs. Remove the stuffing mixture to a bowl and allow to cool.
Season the cavity of the birds with salt and pepper.
Divide the stuffing evenly between the two pheasants' cavities.
Roast the pheasants 25 minutes. Add 1/2 cup white wine to the bottom of the pan. Turn the oven heat up to 425 degrees F and cook another 25 minutes, or until a thermometer inserted in the thickest part of breast registers 160 degrees F. Allow to rest 10 minutes before serving so the juices can redistribute.
Remove the dressing from the bird and serve along side. Garnish the dish with fresh sage leaves.