Stir together the maple syrup, brown sugar, bourbon, water, and salt until the salt and sugar are fully dissolved. Cut the pork belly into 4 equal pieces. Put each piece of pork belly into a heavy-duty, zipper-style freezer bag. Add 1/4 of the sliced jalapenos to each bag. Pour 1/4 of the brine into each bag, squeeze as much air out as possible, seal the bag, then aggressively massage the pork belly so that it is fully exposed to the brine. Place them in a rimmed roasting pan and refrigerate for 3 days, massaging the pork belly in the brine twice a day.