Place a saucepan over a medium heat and add canola oil. Stir in onions, celery, garlic and thyme, and sauté until tender, about 5 minutes. Stir in sweet potatoes and maple syrup, and sauté 2-3 minutes more. Add the breadcrumbs and chicken stock, and season with sea salt and freshly ground black pepper.
Transfer to a greased slow cooker. Cook, covered, on high for 2-3 hours or on low for 3-4 hours.