Position an oven rack in the middle of the oven and preheat to 200°C.
Cut each squash in half lengthwise and scoop out and discard the seeds. Arrange the halves in a large baking dish, flesh-side up.
Whisk together the vinegar, maple syrup and 2 tablespoons oil. Brush the flesh-side of the squash halves with some of the maple-oil and sprinkle with 1/4 teaspoon salt and a few grinds of pepper. Put the squash flesh-side down in the baking dish, then brush the skin side with the maple-oil mixture and sprinkle with 1/4 teaspoon salt and a few grinds of pepper. Roast until the squash is fork-tender, 30 to 40 minutes. Let the squash rest until cool enough to handle. Scoop some of the flesh out into a large bowl, leaving about 1/4-inch border of flesh all around. Leave the scooped-out flesh in relatively large chunks.
Meanwhile, heat 1 tablespoon oil in a medium saucepan over medium-high heat, then add the onions and cook, stirring occasionally, until soft and golden brown, about 6 minutes. Add the rice, curry powder, cinnamon, cayenne and 1/2 teaspoon salt and stir until the spices are toasted, about 1 minute. Add 2 cups water and bring to a simmer covered, stirring occasionally, until the rice is tender and most of the liquid is absorbed, 30 to 40 minutes (different brands of wild rice may vary in cooking times; add more water if needed). Remove from heat and add to the chunks of butternut squash along with the remaining maple-oil, cherries, parsley, sage, 1/2 teaspoon salt and a few grinds of black pepper.
Evenly stuff the scooped-out squash halves with the filling, then drizzle with the remaining 1 tablespoon oil and bake, uncovered, until the filling is warmed through, about 30 minutes. Cut each in half crosswise and transfer to a serving platter. Sprinkle with walnuts and parsley. Serve warm.
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The squash may be baked and stuffed the day before. Finish the baking right before serving.