No, there is not a working trainer for this title. Even though the game was reworked for Steam this past year, the title is still several years old (seven in fact). Our friends at CH are focused on recent titles and the immense amount of patches and updates that come with them. They cannot make trainers for every game so they focus on major modern titles.
All that being said, the console cheats still work in the Steam version of AOE III. So cheating is not out of the question. Just look those up and you will be good to go.