Combine all brine ingredients, except ice water, in a stockpot, and bring to a boil. Stir to dissolve solids, then remove from heat, cool to room temperature, and refrigerate until thoroughly chilled.
Early on the day of cooking, (or late the night before) combine the brine and ice water in a clean 5-gallon bucket or 20-quart stock pot. (If you make the brine the same day you need to use it, just use a 7 lb bag of ice and 2 cups of cold water to chill it down fast.).
Place thawed turkey breast side down in brine, cover, and refrigerate or set in cool area (like a basement) for 6 hours. Turn turkey over once, half way through brining. If not refrigerated, add a couple pounds more ice halfway through to keep it good and cold.
A few minutes before roasting, heat oven to 500 degrees. Combine the apple, onion, cinnamon stick, and cup of water in a microwave safe dish and microwave on high for 5 minutes.
Remove bird from brine and rinse inside and out with cold water. Discard brine.
Place bird on roasting rack inside wide, low pan and pat dry with paper towels. Add steeped aromatics to cavity along with rosemary, sage, oregano, lemon and orange. Tuck wings under breasts and coat whole bird liberally with canola (or other neutral) oil.
Roast on lowest level of the oven at 500 degrees F. for 30 minutes. Remove from oven, pour in 3 cups of broth and scrape up any fond (browned bits) on the bottom of the pan. Cover breast with double layer of aluminum foil, insert probe thermometer into thickest part of the breast and return to oven, reducing temperature to 350 degrees F. After 45 minutes, add 1 more cup of broth. Set thermometer alarm (if available) to 161 degrees. A 14 to 16 pound bird should require a total of 2 to 2 1/2 hours of roasting. Let turkey rest, loosely covered for 15-30 minutes before carving.
For the gravy, strain the turkey pan juices from the roasting pan through a sieve and into a 4-cup glass measuring cup; discard the solids. Spoon off the fat from atop the pan juices. Add enough chicken broth, about 1 to 2 cups, to the pan juices to measure 4 cups total. Melt the butter in a heavy large saucepan over medium-high heat. Add the flour and whisk for 1 minute. Gradually whisk in the broth. Simmer until the gravy thickens slightly, whisking often, about 10 minutes. Season with salt and pepper. Serve the turkey with the gravy.