Cannoneer Whessan is a level 19 human found in Northwatch Hold in the Barrens. He is located (60.5, 54.8) at the third and final tower (the highest) in Northwatch Hold. Captain Thalo'thas Brightsun wants Whessan killed.
Two cannoneers — called Smythe and Whessan — are located at Northwatch Hold. When you put their names together you will find a pun on "Smith and Wesson", a handgun manufacturer.