Preheat your oven to 350F. Cut the cornbread into 1/2-inch cubes. Spread on a large rimmed baking sheet and toast in the oven for about 10 minutes. Flip and toast another 10 minutes, or until the cubes look nicely browned.
Turn oven up to 375F. Butter a 9x13-inch casserole dish. Set aside for now.
Set a large skillet over medium heat. Mix the maple syrup and mustard into the sausage, and then add the canola oil and sausage to the skillet. Stir with a wooden spoon to break up large clumps. Cook until the sausage is nicely browned, 7-10 minutes.
Transfer the sausage to a bowl and pour off any fat drippings. Return the heat to medium.
Add 4 tbsp butter to the same skillet you used earlier, and add the onion, garlic, celery, and a pinch of salt. Cook 5 minutes, or until tender, fragrant, and translucent.
Combine the stuffing ingredients. Add the onion mixture to the cornbread and fold in the browned sausage and stock. Finally, fold in the eggs and sprinkle with parsley.
Bake at 375F for 35-45 minutes, or until piping hot and golden brown on top.