Two to three days before roasting, thaw the turkey in the refrigerator or in a cooler kept at 38°F tops.
Combine the vegetable stock, salt, brown sugar, peppercorns, allspice berries, and candied ginger in a large stockpot over medium-high heat. Stir until the salt and sugar dissolve. Remove from the heat. Cool to room temperature, then refrigerate the brine.
The eve before roasting, combine the brine and iced water in a cooler. Place the thawed turkey (guts, neck, and whatnot removed) breast side down in the brine. Seal up the cooler and use is as an ottoman.
Target brine time: 12 hours; flip the bird once about halfway through.
Roasting day: Heat the oven to 500°F.
Remove the bird from the brine and rinse inside and out. Discard brine.
Place the bird on a roasting rack and place inside a roasting pan. Pat the bird dry (inside and out) with paper towels.
Combine the apple, onion, cinnamon, and water in a microwave-safe bowl. Microwave on high for 5 minutes. Add to the turkey’s cavity, along with the rosemary and sage. Truss, if you like.
Lightly coat the bird with canola oil. Roast the bird on the lowest rack of the oven for 30 minutes.
Insert a probe thermometer into the thickest part of the breast and reduce the oven temperature to 350°F.
Roast until the thermometer registers 155°F, about 2 1/2 hours.
Remove from the oven, cover loosely with aluminum foil, and let rest for at least 15 minutes before carving.