Although it doesn't use any gunpowder weapon, the Tomahawk has both "Musket Infantry" and "Gunpowder unit" tags.
In Age of Empires III, gunpowder units are commonplace due to the game being set in the Age of Discovery through to the early Industrial Age. Nearly all civilizations can train gunpowder units of different kinds, with the only exceptions being the Aztecs and Incas (and even they can obtain some by convertingTreasure Guardians or with the Tupac Rebellion card).
All building and naval fire in the game is depicted as coming from gunpowder weapons like muskets and cannon. The exception are the the four Native American civilizations, who fire arrows.