Combine the marinade ingredients in a sturdy, 2-gallon zipper-lock bag. Add the turkey to the bag and seal.
Set the turkey in the bag, breast side down in a large bowl and place in
the refrigerator overnight.
Place all ingredients in food processor and process until smooth.
Combine glaze ingredients in small bowl and whisk to combine. Add salt and pepper to taste.
To cook turkey: Position rack on the lowest position in oven. Heat the oven to 350 degrees F.
Remove the turkey from the marinade and pat dry. Loosen the skin over the breast, wings, and upper thighs by gently sliding fingers underneath the skin. Rub half the maple butter beneath the skin distributing it evenly.
Rub the remaining maple butter over the outside of the turkey. Stuff the cavity with the onions and celery. Tie the legs together loosely and place the turkey breast side up on the rack.
Roast the bird about 3 hours or until a thermometer reads 180 degrees F.
Baste with maple glaze every 20 minutes. Tent with foil if browned before done.