Wrap seeds, peppercorns, and bay leaves in a square of cheesecloth; tie with kitchen twine. Bring 2 gallons water, the salts, and brown sugar to a boil in a very large pot, stirring to dissolve. Add bundle, garlic, thyme, and parsley. Let cool completely. Fully submerge turkey, weighting it down with a plate topped with cans if necessary. (In lieu of a large pot, you can use a brining bag. Try Turkey Perfect Brine Bag, $4, fireandflavor.com.) Refrigerate the turkey overnight.