Preheat oven to 350°F. Line bottom and sides of a 13- x 9-inch pan with aluminum foil, allowing 2 to 3 inches to extend over sides; lightly grease foil with cooking spray.
Pulse flour, granulated sugar, and salt in a food processor until combined. Add butter cubes, and pulse until mixture is crumbly. Reserve 1 cup flour mixture. Press remaining flour mixture onto bottom of prepared pan.
Bake 25 to 30 minutes, until lightly browned. Spread cherry pie filling over crust in pan. Toss together reserved flour mixture and pecans. Sprinkle mixture evenly over filling.
Bake until golden brown for about 40 to 45 minutes and filling is bubbly. Cool completely in pan on a wire rack, about 1 hour. Lift baked bars from pan, using foil sides as handles.
Stir together powdered sugar, 4 teaspoons milk, and vanilla extract. Add additional milk, if needed, to reach the desired consistency. Drizzle over the top of the bars. Cut into 24 bars.