To prepare streusel, combine first 5 ingredients in a medium bowl; cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal.
To prepare filling, combine pear, cranberries, 2/3 cup brown sugar, and cornstarch in a large bowl; toss well to combine. Spoon pear mixture into pastry shell; sprinkle streusel over pear mixture. Bake at 350° for 1 hour or until bubbly and streusel is browned. Cool at least 1 hour on a wire rack.