In a large bowl, combine cherry pie filling, mixed berries and kirsch. Set aside.
Gently unfold bottom crust onto floured pie dish. Pour berry filling into unbaked crust. Using a pie pan as a guide, cut a circle for the top crust from a sheet of pie crust. Use a lattice cutter to create a pattern, and generously flour each piece so that pieces of lattice do not stick. Top pie with lattice strips and flute the edge of the pie with a fork. Brush top crust with beaten egg and sprinkle lightly with sugar. Bake for 40 minutes, or until bubbling appears in the middle of pie. Cover pie with aluminum foil halfway through baking. Let sit for 20 minutes before serving.