2 to 3 days before roasting: Begin thawing the turkey in the refrigerator or in a cooler kept at 38ºF.
Combine the vegetable stock, salt, brown sugar, peppercorns, allspice berries, and candied ginger in a large stockpot over medium-high heat. Stir occasionally to dissolve solids and bring to a boil. Remove the brine from the heat, cool to room temperature, and refrigerate.
Early on the day or the night before you'd like to eat: Combine the brine, water, and ice in a 5-gallon bucket. Place the thawed turkey breast-side down in brine. If necessary, weigh down the bird to ensure it is fully immersed, cover, and refrigerate or set in cool area for 8 to 16 hours, turning the bird once half way through brining.
Heat oven to 500ºF. Remove the bird from brine and rinse inside and out with cold water. Discard the brine.
Place the bird on a roasting rack set inside a half-sheet pan and pat dry with paper towels.
Combine the apple, onion, cinnamon stick, and 1 cup of water in a microwave-safe dish and microwave on high for 5 minutes. Add steeped aromatics to the turkey's cavity along with the rosemary and sage. Tuck the wings underneath the bird and coat the skin liberally with canola oil.
Roast the turkey on lowest level of the oven at 500ºF for 30 minutes. Insert a probe thermometer into thickest part of the breast and reduce the oven temperature to 350ºF. Set the thermometer alarm (if available) to 151ºF. A 14- to 16-pound bird should require a total of 2 to 2 1/2 hours of roasting. Let the turkey rest, loosely covered with foil or a large mixing bowl, for 15 minutes before carving.