Preheat the oven to 350°F.
In a small saucepan, heat the water, sugar, vinegar, and salt. Place the onion and jalapeños in a heatproof bowl, cover with the vinegar mixture and cool to room temperature.
Heat a large oven-safe braising dish over medium heat with the olive oil. Pat the pork dry and season with salt and pepper. When the oil is hot, add the pork, working in batches to avoid crowding the pan, and sear on all sides. Add more oil as necessary. Turn off the heat.
Add the cloves, chile de arbol, bay leaf, peppercorns, onion, carrots, cumin seeds, pasilla peppers, garlic, chicken stock, orange juice, and beer to the braising dish with the seared pork. Add more stock if necessary so that the liquid comes at least halfway up the sides of the meat. Cover with an inverted lid of parchment paper that touches the top of the beef, and a tightly fitting pot lid. Braise in the oven for 90 minutes to 2:30 hours, until the beef is very tender. Remove the meat from the braising liquid and shred with two forks or you hands, adding liquid as necessary to keep moist.
For the salsa, toss the tomatoes, tomatillos, onions, chiles and garlic on a baking sheet with the canola oil and a pinch of salt. Roast for 15 minutes, until the peppers and tomatoes are sunken. Transfer to a blender and purée until smooth. Adjust the seasoning to taste.
In a small bowl, combine the cotija and sour cream.
To serve, warm the tortillas for 1-2 minutes on an oven rack. Divide the carniats between the tortillas and top with cotija-sour cream, avocado, cabbage, cilantro, roasted salsa and pickled onions and jalapeños.