By Zach Koons The two rival fighters are officially set to square off for a third bout later this year. View the original article to see embedded media. The final fight of the Canelo vs. GGG trilogy is officially on. Canelo Álvarez and Gennadiy Golovkin will square off for a third time on Sept. 17. Both fighters confirmed the news in tweets on Tuesday. The announcement comes after Álvarez had confirmed Monday that an agreement was already in place for a third bout between him and Golovkin. The 31-year-old was expected to exercise his rematch clause to face Dmitry Bivol in September, but instea…