In large bowl, mix together flour, sugar and salt. Using pastry blender or 2 knives, cut in butter until mixture forms small butter lumps (about pea-size). Stirring briskly with fork, add ice water 1 tbsp (15 mL) at a time until dough starts to come together, adding additional water if necessary, 1 tbsp (15 mL) at a time. Form into 2 rounds; shape each into a rectangle 7- x 3-inch (18 x 8 cm). Wrap in plastic wrap and refrigerate for 1 hour. 

Let cold pastry stand for 10 minutes at room temperature. Meanwhile, line 15- x 10-inch (40 x 25 cm) rimmed baking sheet with parchment paper. On lightly floured surface roll out pastry into 17- x 12-inch (43 x 30 cm) rectangle. Place into prepared pan, pressing into corners and sides. Roll out remaining dough to the same size and cut 3/4-inch (2 cm) lengthwise strips for the lattice top.

Filling: In large bowl, mix together 1-1/4 cups (300 mL) of sugar and cornstarch. Stir in cherries and juice; mix well. Spoon over bottom crust. Place lattice strips diagonally across the cherries, about 1/2-inch (1 cm) apart to cover top. Lay remaining strips diagonally the other way, across the first strips. Pinch down ends of strips to secure to pastry edges, Push edges over into the inside edge of the pan. Brush lattice with milk; sprinkle with remaining sugar.

Bake in lower third of 375°F (190°C) oven for 50 to 55 minutes, or until crust is golden and filling is bubbly. Let cool on wire rack for 1 hour. Cut into squares.