Stormwind Cannoneer

The Stormwind Cannoneers are level 65 guards who can be found standing near the cannons in Stormwind Harbor, which they operate.

Trivia

 * Oddly enough, although they wear the exact same armor set as other members of the Stormwind City Guard used to wear, their armor model was not updated in Patch 6.0.2 like the others.

Speculation
They may be a part of the Stormwind Harbor Guards.