Cut any excess fat off of the pork shoulder and then cut it into three large pieces. Season them with salt and pepper.
Heat the canola oil over medium heat in a stock pot or Dutch oven and saute, turning each piece to evenly brown each side.
Remove the pork from the pot and place in a large crockpot and drain off any accumulated fat.
Add the onions to the pot and saute until they are soft. Stir in the garlic and tomato paste and saute for about five minutes. Pour in the wine and scrape the bottom of the pot to deglaze it. Cook for another five minutes and then add the tomatoes, thyme, rosemary and bay leaves, smashing the tomatoes as you stir.
Add the mixture, along with two cups of water, to the pork in the crockpot. Cook for two and one-half to three hours on high or five to six hours on low.
When the pork is done, shred it with two forks, and stir it back into the sauce, adding salt and pepper to taste and removing the bay leaves.
For the polenta, add the milk and chicken stock to a stock pot or Dutch oven and bring to a very low boil. Add the polenta or corn meal, whisking constantly as you add it. Once the polenta is well-combined, place a lid on the pot and remove it from heat. Don't open it again until 20 minutes have elapsed.
Remove the lid and add the butter and parmesan cheese, whisking until everything is well combined. Add salt and pepper to taste.
Serve the ragu over top of the polenta in bowls, topping with a bit more parmesan.