Mix the light brown sugar, ground mustard, paprika, allspice, cayenne, red pepper flakes, 2 tablespoons salt and 1 tablespoon pepper in a small bowl. Rub the spice mix all over the pork roast, including the inside of the crown.
Add all the root vegetables and the onions to a large bowl. Drizzle with the olive oil and sprinkle with the thyme and the remaining teaspoon each salt and pepper. Toss until the vegetables are coated. Mix together the butter with the maple syrup in a small bowl. Set aside at room temperature while the roast cooks.
Place the roast in the center of a baking sheet and arrange the vegetables all around it. Roast, rotating halfway through, until the internal temperature reaches 140 degrees F, about 2 hours. Raise the heat to 425 degrees F.
Add the white wine to the baking sheet, then baste the roast with the maple butter. Continue to roast for 15 minutes more. Remove the roast to a serving platter. Let the meat rest for at least 30 minutes. Remove the vegetables from the baking sheet with a slotted spoon and place them into and around the crown roast on the serving platter. Pour any drippings from the baking sheet into a small saucepan. Add the Dijon mustard and any remaining maple butter to the saucepan. Bring to a boil over medium-high heat and cook until reduced by half and slightly thickened, 3 to 5 minutes. Remove from the heat and add the parsley. Pour the sauce over the roast and vegetables or keep on the side.