Preheat a grill for cooking over medium-high heat (about 375 degrees F) and grease a medium cast-iron skillet with cooking spray or butter. In a medium bowl, whisk together the flour, baking powder, salt and 1/4 cup of the maple sugar. Mix in the milk, vinegar and oil until just combined.
In another medium bowl, toss together the cherries, cornstarch and the remaining 2 tablespoons maple sugar. Transfer the fruit to the prepared skillet and dollop the dough over the fruit; sprinkle with maple sugar. Cover with foil and grill until the juices are bubbling, about 25 minutes; uncover and continue to cook until the top is golden, 15 minutes more. Let cool 5 minutes before serving.