Mix the spices to create the seasoning rub. Set aside 1 tablespoon of the mix. Generously rub the mix all over the pork.
Heat the canola oil over medium-high heat in a skillet large enough for the pork shoulder. Sear the pork on all sides.
Place the pork in the slow cooker. Add in the beer, orange juice, lime juice, onions, garlic, and 1 tablespoon of seasoning mix you set aside in step #1. Do not pour the liquid directly on top of the pork as this could rinse off the seasoning.
Cover the slow cooker and set the temperature. You can set the temperature on high for 4 hours or low for 8 hours.
When the time is up, remover the meat for the slow cooker to a sheet pan.
Pour the liquid and the remainder of the contents into a sauce pan and heat it on medium-high heat. Reduce the liquid to about 1/4 cup. Once that is done, pour the liquid through a sieve or strainer to remove the solid pieces.
Meanwhile, use 2 forks to pull apart the pork. Remove any additional fat and the bone. However, keep any onions that came out with the pork. Return the meat to the slow cooker and add the liquid from the previous set.
Heat the tortillas in sets of 2 as corn tortillas have a tendency to tear. Using 2 usually keeps that from happening. They can be heated on a grill, grill pan, directly on the burners of a gas stove, or in a skillet. You want a little char on them. Be sure to heat both sides, about 2 minutes on each side.
Just before serving, put some of the pork in a skillet over medium heat to brown it a little, about 4 minutes.
To construct the tacos, add about 1/3 cup of pork and top it with some of the suggested topping - pickled onions, radishes, cilantro, queso fresco, jalapenos, and garlic lime sauce. Squeeze fresh line to add to the flavor
Mix all the ingredients in a mixing bowl and set in the refrigerator until the pork is ready to serve.