1Preheat the oven to 425 degrees F (220 degrees C).
2Press one of the pie crusts into a 9 inch pie plate. In a large bowl, stir together 1/2 cup of sugar, cornstarch and cinnamon. Stir in the cherry pie filling and blueberries. Spoon into the pie crust. Top with the second crust, and press the edges to seal. Flute edges, or press with the tines of a fork. In a cup, whisk together the egg white and water with a fork. Brush over the top of the pie, then sprinkle with 2 teaspoons of sugar.
3Bake for 45 to 55 minutes in the preheated oven, or until crust is golden brown. Cover the edges of the crust with aluminum foil if they appear to be getting too dark. Cool for at least 2 hours to allow the filling to set before serving.