Pour water, sodium nitrate, curing salt, coarse salt, brown sugar, and maple syrup into a large kettle. Bring to a boil over high heat and cook for 10 to 15 minutes until everything is well dissolved. Pour brine into a 5 gallon plastic bucket and cool to room temperature, 6 to 8 hours.
Leaving the skin on the pork belly, cut against the grain into 4 to 6 slabs so they fit inside the bucket, and inside your smoker. Place into the bucket of brine, and weigh down with a glass or ceramic dish to keep the pork submerged. Cover and refrigerate for 5 to 7 days, rearranging the pork in the brine daily.
On smoking day, remove pork from the brine and rinse well under cold running water, rubbing to remove all external brine. Pat pieces dry and place onto smoker racks. Allow pork pieces to stand, preferably underneath a fan, until the surface of the meat becomes somewhat dried and notably glossy, 1 to 3 hours depending on air circulation.
Smoke pork belly slabs using wood of your choice at a temperature of 90 to 110 degrees F (32 to 43 degrees C) for 8 to 12 hours. Remove rind before slicing.