To be done ahead of time: In a small bowl, combine brown sugar, seasoning blend, salt, ground annatto, and mix to blend. Cut the pork shoulder into 4 even pieces, coating liberally with sugar and spices, pressing into the meat with your hand. Cover and store in fridge up to 8 hours or overnight.
To make the barbecue sauce, combine all ingredients in the Instant Pot. Give a quick stir to blend, then fasten lid. Select PRESSURE COOK and set timer to 3 MINUTES. After 3 minutes, Quick Release the pressure and carefully remove lid. Transfer sauce to a heatproof container to cool. Using a stand or immersion hand blender, blend sauce until smooth. Set aside and cover until ready to use.
Remove seasoned pork from fridge and let come to room temp, about an hour. Pre-heat dutch oven over high heat until extremely hot. Add 1-2 tablespoons of oil and sear the pork pieces until nicely browned, about 3-4 minutes per side. Remove pork and set aside. Add onions and garlic, and continue to saute another minute, and cut heat to low. Deglaze with about a half cup of the stock, scraping free the brown bits from the bottom of the pot. Add the rest of the stock, the orange juice, cider vinegar, and place the pieces of pork snugly in the braise bath. The liquid should come about halfway up the pork.
Securely place the lid and let braise 5 hours. After three hours, check to ensure the braising liquid level still reaches about halfway up the meat. If necessary, add more stock throughout cooking. After 5 hours, remove pork from braise and transfer to a large mixing bowl. The meat will try and fall apart before you make it to the bowl, so be swift and be gentle. With two forks or a fork and tongs, pull the pork to desired consistency. Add about a quarter cup of braising liquid as you toss the pork. Top with cherry barbecue sauce and serve.