Combine first 3 ingredients in a bowl, stirring with a whisk until sugar and salt dissolve. Pour water mixture into a large zip-top plastic bag. Add tarragon, rind, juice, and pork to bag; seal. Marinate in refrigerator 2 hours, turning bag occasionally.
Remove pork from bag; discard marinade. Sprinkle pork evenly with pepper. Place pork on a grill rack coated with cooking spray. Grill 3 minutes on each side or until desired degree of doneness.