Set slow cooker to medium or high for a total cook time of 4 to 5 hours.
In a deep skillet over medium, heat canola oil. Add cubed beef and brown. Remove and add to slow cooker.
Add beef sausage and brown. Remove and add to slow cooker.
Drain half the fat from the pan. The add onion, celery, peppers, chili powder, cumin, oregano, mustard seeds and red pepper flakes to remaining fat and sauté until browned and fragrant. Add to slow cooker.
Reduce heat and add cider vinegar and beef broth, careful as mixture may bubble up. Stir to scrape up all the brown bits from the bottom of the pan. Pour hot liquid into slow cooker.
Stir black, pinto and kidney beans into the slow cooker mixture, combining well.
Add crushed tomatoes, and enough boiling water just to cover mixture, no more.
Cover and cook for 5 hours, check that beans are fully cooked and continue cooking until beans are tender, if required.