Many Jewish websites, (Aish, Jewish History, Ou), state that the the Men of the Great Assembly finalized the contents of Tanach in the early Second Temple Period. No source is brought to support this statement in any of the sites I have perused.
Wikipedia, and Jewish Virtual Library, on the other hand, make no claim that these Sages sealed the Biblical Canon, only that they contributed to it significantly. They bring sources from the Talmud.
A mishnah in Yadayim 3:6 showcases an argument about the ritual status of certain books. This could imply that the last Sanhedrin in Yavneh was still deliberating on certain books' place in Tanakh, though it is not conclusive.
What is the source for the claim that the Men of the Great Assembly Canonized Tanach? I am looking for any source that supports the claim with evidence, or strong evidence found by the Mi Yodeya community. The earlier the better.