Make the glaze: Whisk the maple syrup, mustard, horseradish and chile powder in a bowl and season with salt and pepper. Cover and let sit at room temperature at least 30 minutes to allow the flavors to meld. (The glaze can be made up to 2 days in advance; store, covered, in the refrigerator. Bring to room temperature before using.)
Prepare the turkey: Remove the turkey from the refrigerator 1 hour before roasting. Preheat the oven to 450˚ F. Season the cavity of the turkey with salt and pepper. Rub the outside of the turkey with the butter and season liberally with salt and pepper. Put 4 cups chicken stock in a medium saucepan and keep warm over low heat.
Place the carrots, celery and onions in a large roasting pan and place a roasting rack on top. Put the turkey on the rack, place in the oven and roast until light golden brown, about 45 minutes. (Tent the turkey loosely with foil if it is browning too quickly.) Reduce the oven temperature to 350˚ F, baste with 2 cups warm stock and continue roasting, basting with 2 more cups warm stock halfway through, until an instant-read thermometer inserted into the thigh registers 155˚, about 1 hour. After the turkey reaches 155˚ F, begin basting with the maple glaze; continue roasting, basting with the glaze every 10 minutes, until an instant-read thermometer inserted into the thigh registers 165˚ F, about 20 more minutes.
Remove the turkey from the oven and transfer to a large cutting board. Tent loosely with foil and let rest at least 45 minutes before slicing. Strain the drippings into a bowl and discard the solids. Add enough of the remaining chicken stock to make 6 cups liquid.
Make the gravy: Melt the butter in a medium saucepan over medium heat. Whisk in the flour and cook until light golden brown, about 8 minutes. Slowly whisk in the stock-drippings mixture, then bring to a boil and whisk until the gravy begins thickening and the flour taste has been cooked out, about 10 minutes. Add more stock until you reach the desired consistency. If desired, add a splash of white wine and cook 2 more minutes. Stir in the herbs and season with salt and pepper.
Heat the remaining stock in a saucepan over low heat. Remove the turkey legs and wings, then remove the dark meat and shred. Remove the breasts and cut crosswise into 1-inch-thick slices. Ladle some of the warm stock on top of the turkey and serve with the gravy.