For filling, in a large saucepan, combine fruit and water. Bring to boiling; reduce heat. Simmer (do not simmer raspberries), covered, about 5 minutes or until fruit is tender. Combine the 1/2 cup sugar and the cornstarch; stir into fruit. Cook and stir over medium heat until mixture is thickened and bubbly. Cook and stir for 2 minutes more; set filling aside.
Preheat oven to 350 degrees F. In a bowl, combine the 3 cups flour, the 1-1/2 cups sugar, the baking powder, and baking soda. Cut in 1/2 cup butter until mixture resembles coarse crumbs. Make a well in the center of the flour mixture; set aside.
In another bowl, combine eggs, buttermilk, and vanilla. Add egg mixture all at once to flour mixture. Stir just until moistened (batter should be lumpy). Spread half of the batter into an ungreased 13x9x2-inch foil baking pan. Spoon and gently spread filling over batter. Drop remaining batter in small mounds onto filling.
In a bowl, stir together the 1/2 cup flour and 1/2 cup sugar. Cut in the 1/4 cup butter until mixture resembles coarse crumbs. Sprinkle over coffee cake.
Bake for 45 to 50 minutes or until golden. Cool completely on a wire rack.