Attack On Titan appears to use a mix of technology from different eras. The flying rigs and gear used by the military appear to be advanced technology, but they use cannons to defend the city against the titans.
Most of the city appears to use roughly 17/18th Century technology.
In the TV series we're only told that the Titans appeared 100 years earlier, and wiped out most of humanity. The Titans themselves appear to be the product of some kind of advanced technology too.
From this it could be inferred that the series is set in our distant future, but there's nothing to show this for certain. It could be an alternate history story.
Is there anything in canon (from the manga/anime) that tells when the series is set, relative to our own history/calendar?