Line a sheet pan with parchment paper. Spray the parchment paper with cooking spray. Shingle the bacon strips side-by-side on the parchment paper, allowing the edges to overlap slightly. Refrigerate until ready to use.
Butter each side of the bread slices, using 2 tablespoons butter in total. Place the bread in a 9-by-13-inch baking dish. Set aside.
Mix the remaining 4 tablespoons butter with the sage, maple syrup, salt, garlic powder, onion powder and pepper in a bowl. Use your fingers, and a knife, if necessary, to make a pocket between the meat and the skin of the turkey. Rub the butter under the skin in an even layer. Place the sheet pan with the bacon on a work surface, then lay the turkey skin-side down on the bacon. Wrap the bacon around the turkey by lifting the parchment and pressing the bacon against it to secure. Place the turkey skin-side up on top of the bread and lift away the parchment.
Roast until the internal temperature reaches 165 degrees F, 1 1/2 to 2 hours. Let rest for 30 minutes before slicing. Quarter the stuffing croutons before serving. Serve warm.