Preheat the oven to 350 degrees . Grease a 9-by- 13-inch baking dish. Spread the bread cubes on a baking sheet and bake until lightly toasted, about 10 minutes. Transfer to a large bowl.
Meanwhile, in a large skillet, melt the butter over medium-high heat. Add the celery and scallions and cook, stirring occasionally, until softened, about 5 minutes. Scrape into the bowl with the bread and add the chicken broth, oysters with liquid, parsley, tarragon, paprika, 1 1/2 tsp. salt and 1/2 tsp. pepper. Mix well and transfer to the prepared baking dish. Cover with greased foil and bake until hot, about 35 minutes. Uncover and bake until browned and crisp, about 15 minutes.