Combine first 7 ingredients together and rub all over pork roast. Place roast in a slow cooker. Pour in water. Cook roast on HIGH 4-6 hours or LOW 10-12 hours or until roast falls apart easily with a fork.
Remove roast from cooker. Discard cooking liquid. Shred pork and place back in cooker. Add in barbecue sauce. Continue cooking on HIGH 30 minutes or until heated through.
Meanwhile, combine coleslaw mix and dressing.
Serve pork on buns topped with coleslaw and crispy onions.