To make glaze:
In a food processor, combine the butter, maple syrup, lemon juice, the lemon zest, pepper and salt. Process until well blended and transfer to a bowl (the maple glaze can be made in advance and refrigerated, bring to room temperature before using).
Marinate the turkey for 24 hours before cooking.
To marinate:
1. Combine the lemon juice, maple syrup, oil, shallots, garlic, thyme, sage leaves, lemon zest, and pepper in a small bowl and mix well.
2. Place the turkey in a large sturdy 2-gallon plastic bag. Pour the marinade over the turkey and squeeze out as much air as possible and seal the bag. Distribute the marinade evenly over and inside the turkey. Set the turkey breast side down in the refrigerator and marinate for 24 hours, turning occasionally.
3. Preheat the oven to 450 degrees. Position the rack near the bottom of the oven.
4. With a spoon wipe off the shallots and garlic from the turkey. Strain the marinade into a bowl and set the herbs, garlic and shallots aside separately.
5. Using your fingers, carefully loosen the turkey skin over the breast and thighs. Rub all but 3 tablespoons of the softened maple glaze under the breast and thigh skin, patting gently to spread the glaze.
6. Put one third each of the diced onions and celery in the cavity. Tie the legs together with kitchen string and set the turkey, breast side up, on a rack in a large roasting pan.
7. Brush the breast and thigh with the remaining maple glaze and roast for 30 minutes, basting twice. The skin may appear dark in patches because the maple syrup in the marinade caramelizes as the turkey cooks; cover the turkey loosely with foil to keep the skin from burning.
8. Lower the oven temperature to 350 degrees. Spread the remaining onions and celery around the turkey and continue to roast for 1-�½ hours longer or until an instant read thermometer inserted in the thickest part of the breast just above the joint reaches 165 degrees and the juices run clear.
9. During the last 30 minutes, add the reserve shallots, garlic, and herbs to the pan, remove the foil from the turkey and brush twice with the maple glaze.
10. Transfer the turkey to a carving board. Remove the whole legs from the turkey, cutting them off at the hip. Cut the wings from the breast.
11. Return the legs and wings to the pan and roast for about 30 minutes longer until an instant read thermometer reaches 180 degrees and the juices run clear. Meanwhile cover the breast with foil.