Melt butter in a large skillet over medium-high heat; saute leeks, celery, and carrot for 3 minutes. Add mushrooms; saute until tender, 5 to 10 minutes. Add shallots and herbes de Provence; saute until fragrant, about 2 minutes. Pour chicken stock over vegetable mixture and bring to a simmer; season with salt and pepper.
Mix bread crumbs and vegetables mixture together in a bowl. Set stuffing aside to cool.
Cut turkey breast from one side through the middle horizontally to within one-half inch of the other side. Open the 2 sides and spread them out like an open book and pound to an even thickness. Spoon stuffing down the middle of the butterflied turkey. Roll turkey around stuffing and secure with twine. Place in a baking dish and cover with aluminum foil.
Cook turkey breast until no longer pink in the center and the juices run clear, 45 minutes to 1 hour. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C). Remove from the oven and allow turkey to rest for 10 minutes before removing twine and slicing. Serve with cranberry sauce.