Add ketchup and apple cider vinegar to a bowl. Stir until well incorporated. Add maple syrup (or brown sugar), paprika, garlic powder, onion powder, salt and pepper. Mix well, then add onions and mix well.
Fit crockpot with a liner. Add a few spoonfuls of the sauce to the bottom of the crock pot.
Add pork roast and pour remaining sauce all over the top.
Cover and cook on HIGH for 5-6 or LOW for 8-9 hours (until fork tender). Remove pork from bowl and shred with two forks.