To make the brisket, whisk the smoked paprika, onion powder, garlic powder, pepper, coriander, Worcestershire sauce cayenne, kosher salt, and brown sugar in a bowl.
Next, pour the wet rub onto the brisket, massage it into the meat, wrap it with plastic wrap, set it on a rimmed cookie sheet, and refrigerate it overnight.
To make the whiskey maple BBQ sauce, add the diced onion andwhiskey to a pot, heat the BBQ sauce over medium-high heat until it comes to a boil, and cook the whiskey onion mixture for 10 minutes.
Whisk in the ketchup maple syrup, lemon juice, Worcestershire sauce, Dijon mustard, and liquid smoke, decrease the flame to medium-low and cook the BBQ sauce for 25 minutes, periodically stirring until it thickens up.
Let the whiskey maple BBQ sauce cool completely, pour it into a fine-mesh sieve set over a bowl, then cover it with plastic wrap and refrigerate it overnight.
Arrange the oven's rack in the middle of the oven, then program the oven to 260°F.
Place the marinated brisket into a roasting pan with a roasting rack fat side up and cook it for 2-3 hours.
Flip the brisket over and cook it for another 2-3 hours until it has a temperature of 180°F.
Allow the brisket to sit for 1 hour before slicing and serving with the whiskey maple BBQ sauce.