So... is Wonder 3 finished or not?
NO, it is not finished.
Why?
The anime finished after the manga:
Anime finished: June 11, 1999
Manga finished: May 08, 1966
... But MangaUpdates contains information about the anime adaptation and indicates that it is incomplete.
Watching Order (by release date)
Here you have all the anime relations we detected ordered by release date, so you can see the reason for this status in context and also use it as watching order.
The mangas and the non-core contents are excluded by default, but you can enable them by clicking the buttons below:
Wonder 3
The Amazing 3
Anime - Base
Release date: June 06, 1965
Tezuka Osamu no Uchuu Wonder 3: Ginga Renmei no Shisha
手塚治虫の宇宙 W3（ワンダースリー）〜銀河連盟の使者〜
Anime - Adaptation
Release date: June 11, 1999
Synopsis
Wonder 3 follows the journey of three extraterrestrial agents, Bokko, Nokko, and Pukko, who are tasked with a crucial mission: assessing the threat Earth poses to the wider universe.
Disguised as Earth creatures – a rabbit, a horse, and a duck respectively – they must observe humanity and determine if the planet warrants destruction via a powerful, planet-ending weapon.
Traveling in their unique, high-speed vehicle, the Big Wheel, the trio explores the world, grappling with complex issues like ecological damage and widespread poverty, as they try to decide Earth's fate.
The series highlights their observations and internal conflicts as they weigh the potential dangers and merits of a planet on the brink.