Preheat oven to 350°. In a greased 13x9-in. baking dish, combine sweet potatoes, carrots and plums. Combine orange juice, water, honey, brown sugar and cinnamon; pour over vegetables. , Cover and bake for 1 hour. Uncover; dot with butter. Bake until vegetables are tender and sauce is thickened, 45-60 minutes, carefully stirring every 15 minutes.