I love to spatchcock turkey (or chicken). You get the same roasty flavor you would if you baked the turkey whole, but with the added benefit of it taking much less time to cook. When making the marinade, be sure to puree it as finely as possible so the vegetables don't get stuck in the injecting tool.
Combine the butter, wine, celery, bell pepper, onion, Cajun seasoning, brown sugar, hot sauce and salt in a food processor or blender. Process until very smooth. Transfer the mixture to a saucepan and keep warm over low heat.
Remove the giblets and neck from the turkey and save for stock or discard. Place the turkey breast-side down on a cutting board. Cut along one side of the backbone from the tail to the neck with a chef's knife or kitchen shears. Repeat with the other side and remove the backbone. (Save for stock!)
Turn the turkey over, and press down on the breastbone with the heel of your hand until it cracks. Tuck the wing tips up and over the back of the turkey. (This prevents them from burning.) Place the turkey on a wire rack in a roasting pan.
Fill a flavor injector with the butter mixture and inject as much of the butter into the turkey at different angles. Pour any remaining butter over the top of the turkey, then sprinkle with additional Cajun seasoning, if desired. Place the roasting pan on the middle rack in the oven and bake for 30 minutes, undisturbed.
Baste the turkey with the pan juices and reduce the oven temperature to 350 degrees F. Continue to bake, basting occasionally, until a meat thermometer reaches 165 degrees F when inserted in the thickest portion of the breast and thigh (avoiding bone), 45 minutes to 1 hour. (Add the chicken stock to the roasting pan if it starts to dry out.) Let rest before slicing. Serve with the pan drippings.