Preheat oven to 400°F (200°C). Line a rimmed baking sheet with foil. Cut each acorn squash in half from stem to tip, scoop out seeds, and score the flesh in a crosshatch pattern. Place cut-side up on the baking sheet.
Melt butter with maple syrup. Brush generously over the cut surface and cavity of each squash half. Season with salt and pepper. Drizzle with 1 tablespoon olive oil.
Roast the squash at 400°F for 25 minutes until partially tender and golden around the edges. Remove from oven and set aside.
Heat remaining 1 tablespoon olive oil in a large skillet over medium-high heat. Add sausage, breaking into crumbles, and cook 6-8 minutes until browned. Transfer to a paper towel-lined plate, leaving drippings in the pan.
Reduce heat to medium. Add onion and celery to the skillet and cook 4-5 minutes until softened. Add garlic and cook 1 minute until fragrant.
Add apple to the skillet and cook 2-3 minutes until slightly softened. Return sausage to the pan. Stir in cooked rice, dried cranberries, sage, thyme, smoked paprika, salt, and pepper. Remove from heat and stir in Parmesan cheese.
Divide the filling evenly among the four par-roasted squash halves, mounding it generously. Sprinkle with additional Parmesan cheese if desired.
Return to the oven and bake 20-25 minutes until squash is fork-tender and filling is golden. Broil for 2-3 minutes for extra browning if desired.
Remove from oven, let rest 5 minutes, then garnish with fresh parsley before serving.