Score the duck breasts. Mix together apple juice, salt, pepper, Chinese 5 spice, vinegar, and honey. Soak the duck breasts in the brine for 3 hours.
While the duck is in the brine, make a small sachet by tying juniper berries, peppercorns, and thyme in cheesecloth.
In a small saucepan, combine vinegar and water. Heat the mixture over low heat. Add the sugar and stir to dissolve. Add the sachet and cranberries. Remove from heat and chill for 1 hour.
Drain cranberries, reserving 2 tablespoons of the brining liquid. Discard sachet.
Heat oil in a pan over medium heat. Add shallots and cook until translucent. Add apples. Cook for 1-2 minutes. Deglaze pan with brining liquid. Stir in cranberries. Remove from heat and let cool.
Pack cranberry relish in glass jar or jars. Pour pickling liquid over the berries. Store in a cooler or fridge for 3 hours or up to 1 week. Can in water bath canner for longer storage.
Heat the smoker to 250 degrees. Remove the duck breasts from the brine. Rinse in water and gently pat dry. Smoke duck for 1 hour or until the internal temperature reaches 145 degrees.
Heat cast iron pan over high heat. Add duck breast and sear skin side down for 2-3 minutes. Remove the duck and let rest for 5 minutes.
Thinly slice duck breast. Serve with pickled cranberry relish.
