Prepare baking sheets and oven: Place 2 large rimmed baking sheets on upper third and lower third racks in oven. Preheat oven to 450°F.
Prepare squash: Stir together butternut squash, brown sugar, 1 tablespoon of the oil, and ½ teaspoon of the salt in a large bowl until coated. Carefully remove baking sheet from lower oven rack; spread squash evenly on baking sheet.
Prepare sprouts: Combine Brussels sprouts, remaining 2 tablespoons oil, and remaining ½ teaspoon salt in same large bowl. Carefully remove baking sheet from upper oven rack; spread Brussels sprouts evenly on baking sheet.
Bake squash and Brussels sprouts: Bake squash in preheated oven on lower rack until tender and browned in spots, 20 to 25 minutes, rotating baking sheet front to back halfway through. Bake Brussels sprouts on upper oven rack until browned and crisp, 25 to 30 minutes, stirring and rotating baking sheet front to back halfway through.
Heat up maple-butter mixture: Place maple syrup and butter in a small microwavable bowl, and microwave on HIGH in 20 second intervals, stirring after each interval, until butter melts and mixture is warm; stir in crushed red pepper.
Toss vegetables with pecans, cranberries, and maple-butter mixture: Transfer squash and Brussels sprouts to a large bowl; stir in pecans, cranberries, and maple-butter mixture. Serve warm.
