Add pork shoulder, beer, garlic powder, cayenne pepper, paprika, cumin, pepper, and salt to the insert of a slow cooker. Set slow cooker to low and cook for 10 hours. Using two forks, pull apart the pork shoulder until all of it has been shredded. Set aside and keep warm.

In a medium bowl, combine corn kernels, red onion, jalapeño, lime juice, salt, and pepper. Toss to combine. Set aside.

In a small skillet, add canola oil until about 1 inch deep. Heat oil over medium-high heat. Once the oil is hot and shimmering, fry corn tortillas one at a time, until golden brown, approximately 1-2 minutes per side. Remove to a paper-towel lined plate to drain and sprinkle with salt. Repeat with the remaining tortillas.

To build your tostadas, slather the crispy corn tortilla with a thick layer of pulled pork. Top with guacamole, corn salsa and a sprinkle of queso fresco. Serve immediately.