Remove and discard giblets from hens. Rinse hens well; pat dry with paper towels. Remove skin with sharp knife; trim excess fat. Split hens in half lengthwise; set aside. To make rice stuffing, heat medium saucepan coated with cooking spray over medium-high heat. Add onion, mushrooms, and garlic; sauté until golden brown. Add rice, seasoning packet, and 2 1/4 cups water (omit butter or oil). Follow package instructions to cook rice. Preheat oven to 400°. Coat 9 by 13-inch casserole dish with cooking spray, then place four 1/2 cup mounds of rice in dish. Fit Cornish hen halves over top of rice and press down. Roast hens at 400° for about 20 minutes. While hens are cooking, prepare glaze by stirring together all ingredients. After hens have cooked for 20 minutes, remove from oven and brush with maple glaze. Continue to roast for an additional 15 minutes or until juices run clear, brushing once more with glaze. Pepper to taste.