Place the pork in 3- to 4-quart slow cooker. Sprinkle with the Mexican seasoning and brown sugar. Drizzle with 2 tablespoons cider vinegar.
Cover and cook on high for 4 to 4 1/2 hours, or on low for 8 to 9 hours until the pork is fork-tender and can easily be pulled apart.
Remove the pork and discard liquid. Using a fork, shred the meat and return to the slow cooker. Toss the pork with barbecue sauce.
Combine the coleslaw mix and green onions in a large bowl.
Whisk the sour cream, mayonnaise, horseradish, 1 teaspoon cider vinegar, mustard, salt and pepper in a small bowl until blended. Stir into the coleslaw mixture.
Serve the shredded pork on sandwich buns, topped with the coleslaw.