Set up your grill for indirect heat. Open all vents, remove top grate from your grill, and light between 1/2 and 2/3 of a chimney of charcoal.
Prep your turkey by removing the plastic truss and pop-up timer and clear the cavity. Rinse with water and pat dry with paper towels. Set on a rimmed baking sheet to transfer to the grill.
Strip the leaves from the thyme and rosemary. You should have about 1 1/2 tablespoons of each. Mince the leaves along with the sage.
Mix the sage, thyme, rosemary, garlic, 2 tsp Montreal Chicken seasoning, and ½ tsp black pepper in a small bowl. Add the butter and mix into a paste.
With your fingers or a wooden spoon handle, carefully loosen the skin of the turkey and rub the butter paste all under the turkey skin. Season the outside of the turkey with remaining ½ tsp black pepper and 1 teaspoon Montreal Chicken seasoning or Kosher salt.
Open beer and drink or pour out 1/3. With a can opener, remove entire top of beer can. Place enough onion in the beer can to bring the liquid to 1 inch from the top. Place beer can on rimmed baking sheet. Place the turkey cavity over the beer can and slide turkey, legs down, onto the beer can. Slide legs forward to balance the turkey creating a tripod. Loosely tent the turkey with aluminum foil to transfer to the grill.
Place a medium disposable aluminum roasting pan in the bottom of your grill and fold to fit under the turkey. Place turkey, legs down, inside aluminum pan and make sure it is steady. Pour lit charcoal in grill on either side of aluminum pan. Remove aluminum foil tent from the turkey.
Close the lid and cook turkey 1 hour. Remove lid and evenly add 1/3 chimney unlit charcoal on top of lit charcoal. Close lid and cook 45 minutes. Remove lid and check turkey temperature. Remove from grill when temperature reads 160 degrees F. About 2 – 3 hours total. Temperature will increase as turkey rests.
Turkey is cooked through when temperature reads 165 in the innermost part of the thigh or thickest part of the breast meat.
Let rest 30 minutes before carving and serving.
Notes
Fill the charcoal chimney with about 50 briquettes for 1/2 to 2/3 full.Adding lit charcoal to the grill before placing the turkey can cause burns. When adding the lit charcoal, the aluminum foil tent keeps ash off your turkey.Nutritional values vary depending on the type of turkey meat and whether you eat the skin.