Bring broth, rice, 1 tablespoons butter and seasonings to a boil in a large saucepan. Reduce heat and simmer, covered, for 50 minutes. Remove from heat; let stand for 5 minutes, then fluff with a fork.
Meanwhile, preheat oven to 375°F Melt remaining 2 tablespoons butter in a large skillet. Add onion; saute' over medium heat for 10 minutes, stirring frequently. Add carrots and cook for 5 minutes more. Remove from heat; stir in celery and cranberries. Season to taste with salt and pepper.
Spray a 2 quart casserole dish with olive oil spray. Stir together rice and vegetables. Place in prepared dish and sprinkle with walnuts. Tent loosely with foil and bake for 20 minutes. Remove foil and bake for 10 minutes more.