In a blender or food processor, working in 2 batches, add the achiote paste, bitter orange juice or its substitute, chicken broth, garlic, oregano, cumin, allspice, salt, and pepper and puree until smooth.
Slide the turkey, with the breast side down, into the brining bag. Pour the marinade into the bag and massage it into the bird, working it into the cavity and all the crevasses. Place the bag in a mixing bowl or roasting pan and refrigerate for 12 to 48 hours, turning the turkey a couple of times to redistribute the marinade.
To make the turkey:
Set the oven rack at the lowest position and preheat the oven to 450 degrees Fahrenheit.
Spread the onions and tomatoes in a large roasting pan. Sit the turkey on the vegetables breast side up. Stuff the main cavity with as much stuffing as it can hold and place the rest in a buttered baking dish. Close the cavity by crossing and tying the legs with butcher’s twine. Tuck the wing tips under the turkey. Pour as much of the remaining marinade over the turkey as will fit halfway up the pan.
Roast the turkey for 30 minutes. Cover the turkey with layers of banana leaves, if you are using them, and then cover the entire pan with aluminum foil, sealing it as best as you can. The less steam that is able to escape the better.
Reduce the oven to 350 degrees Fahrenheit. Place turkey back in the oven and roast for 3 1/2 hours, or for at least 12 minutes per pound. Remove from the oven and carefully remove the leaves and/or the foil, being careful as the steam is hot. Return to the oven and roast for 20 more minutes. The turkey should be completely cooked through and nearly falling off the bone.
Remove turkey from the oven and let it rest for at least 15 to 20 minutes, loosely covered with the aluminum foil.
Strain all the cooked vegetables and juice into a medium 3-quart saucepan, pressing with the back of the spoon to get as much liquid as possible. Set aside 1 cup for the stuffing. Simmer the remaining sauce for 15 to 20 minutes, until it has reduced by half.
While the turkey rests, pour the reserved marinade over the stuffing in the baking dish and place it in the oven for 20 minutes, or until it is hot and the top is crisped.