Lightly grease a shallow baking pan. Sprinkle the roasting rub onto all of the surfaces of the chicken; rub in with fingers. Place chicken, skin side up, in prepared baking pan. Roast, uncovered, in a 425 degree F oven for 30 to 35 minutes or until chicken is no longer pink (170 degrees F).
Meanwhile, in a large skillet, cook onions, covered, in hot butter over medium-low heat about 15 minutes or until onions are tender, stirring occasionally. Uncover; add brown sugar. Cook and stir over medium-high heat about 5 minutes more or until onions are golden. Add apple, pear, cranberries, garlic, rosemary and pepper to skillet. Cook, covered, for 5 minutes, stirring twice. Stir in cranberry juice and dry sherry. Simmer, uncovered, for 2 to 4 minutes or until liquid is reduced by half.
To serve, transfer the chicken to a serving platter. Spoon onion mixture over chicken. If you like, serve with steamed green beans.