For Filling: in a small mixer bowl combine cream cheese,1/2 cup cheese and wine. Beat with an electric mixer until almost smooth. Stir in crab meat and shrimp.
In a heavy skillet heat cooking oil. Dip tortillas, 1 at a time, in hot oil for 10 seconds or just till limp, adding more oil if needed. Drain on paper towels.
Spoon about 1/4 cup filling onto each tortilla, then roll up. Place the filled tortillas, seam side down, in a 13x9x2-inch baking dish.
In a medium saucepan cook onion in butter or margarine until tender but not brown. Stir in flour, salt and pepper. Add milk all at once. Cook and stir until thickened and bubbly. Pour sauce over tortillas.
Bake, covered, in a 350° oven for 15 to 20 minutes or till heated through. Remove foil and top with cheese. Return to oven and bake about 5 minutes more or till cheese melts.
Makes 6 servings