In a mixing bowl, toss the onions with the vinegar and season with salt and pepper. Spread the coated onions on a sheet pan and roast in the oven until tender, about 15-20 minutes. In a large, oven-safe mixing bowl, toss the diced bread with 1 tablespoon of the olive oil and season with salt and pepper. Place the bread in the oven and toast until crispy, about 7 to 8 minutes.
While the bread and onions are cooking, set a large sauté pan over high heat and heat the canola oil until it begins to smoke. Add the sausage and cook while crumbling it up with a spoon. When the sausage is completely cooked, remove it from the pan and drain on a paper towel. Discard half of the grease in the pan and save the rest.
Turn the oven to 375 degrees. Once the onions are cooled, roughly chop them to about a half-inch in size. Take the toasted bread, roasted onions, cooked sausage, remaining 2 tablespoons of olive oil and the remaining ingredients and mix together in a large bowl. If cooking inside of a turkey, place the stuffing inside the chest cavity and cook until the turkey is done. If cooking the stuffing separately, place the mix in a large casserole dish, cover with tin foil, and bake for 20 to 25 minutes. Remove the tin foil and bake for another 5 to 10 minutes so that it is slightly crispy on top. Serve hot.