Most of the Cuban-style pork I've made has been whole shoulder (unseparated butt & picnic) roasted using an adobo-style (wet) rub and/or marinade. Often has a lot of acidic liquid (sour orange, lime, vinegar, etc.) that you may not want to use when smoking. Below are a couple of less acidic options that should give you a starting point for a smoked version. As you can see, cumin, oregano, garlic, salt, and pepper sort of define the theme. You'll want to make a paste of the ingredients and rub into the butt the night before your cook. Or you could make a dry version of the rub and use as you would for any smoked butt.
1 large onion, quartered
6 or more cloves garlic, peeled
2 tablespoons fresh oregano leaves or 1 tablespoon dried oregano
1 tablespoon ground cumin
1 teaspoon ancho or other mild chili powder
1 tablespoon salt
2 teaspoons freshly ground black pepper
Olive oil as needed
1 tablespoon wine or cider vinegar
or
8 cloves of garlic, minced
1/4 cup olive oil
2 tablespoons kosher salt
2 tablespoons white wine vinegar
1 tablespoon dried oregano
2 teaspoons freshly ground black pepper
1 teaspoon cumin
