An unnamed X-Men film will reportedly begin production in Montreal in May 2017. According to Le Journal De Montreal, set construction will begin in January.
Several recent X-Men movies were filmed in Montreal, including X-Men: Days of Future Past, and X-Men: Apocalypse. No further details about the reported film are known, however 20th Century Fox has several upcoming dates blocked out for Marvel and X-Men related films, including October 6, 2017, March 2, 2018, and November 2, 2018.
Fox has several X-Men projects known to be in various stages of production, including New Mutants, X-Force, Gambit, and Deadpool 2. Whether this reported project is any of these, or an as yet unannounced film is unknown.