Combine potatoes, carrots, and onion in the bottom of a slow cooker.
Heat canola oil in a large skillet over medium-high heat. Cook beef roast in the hot oil until browned completely, 2 to 3 minutes per side; place beef roast atop the vegetables.
Stir tomato sauce, brown sugar, Worcestershire sauce, cider vinegar, and salt together in a bowl; pour over the roast.
Cook on Low for 10 to 12 hours (or on High for 5 to 6 hours).
Remove roast and vegetables to a serving platter. Pour sauce into skillet and cook over medium-high heat until thickened, 5 to 10 minutes; serve with the beef and vegetables.
