Remove the packaging from the turkey breast and discard any extra turkey parts that came with the turkey. Set the turkey aside.
Make the turkey breast brine. Add 12 cups of cold water to a large 5 gallon bucket or pot. Remove 2 cups of water from the bucket and add it to a small saucepan. Add the salt to the water and whisk.
Bring the water to a boil over high heat and allow the mixture to boil until the salt has dissolved completely.
Add the salt water to the bucket and stir to combine. Add the thyme, rosemary, and half of the white onion to the bucket of water. Place the turkey breast in the bucket of water. Be sure the turkey breast is submerged in water. Refrigerate the turkey overnight to brine.
The next morning, preheat the smoker to 240ºF* and remove the turkey from the brine and rinse it under cold water. Pat the turkey dry with paper towels.
Season the turkey breast with the turkey seasoning on both sides. Massage the turkey seasoning into the turkey. Add the other half of the chopped white onion into the cavity of the turkey. Set aside.
Add orange juice and apple cider vinegar into a spray bottle. Shake to combine.
Place the turkey on the smoker and smoke the turkey breast for 2 ½ - 3 hours, spritzing the turkey breast with orange juice every 30-45 minutes.
Remove the turkey breast from the smoker when the internal temperature reaches 165ºF. Let the turkey breast rest for 10-15 minutes before slicing.