Monster Hunter XX is an expanded version of Monster Hunter Generations that was originally only announced for the Nintendo 3DS. Generations was released in the west in July 2016, some eight months after its Japanese launch.
Capcom has not yet announced a release date for Monster Hunter XX on 3DS or Switch. It also hasn't confirmed that they will be available outside of Japan. Historically, however, Monster Hunter games are localized and made available in other territories, they just take a little extra time to come out.
The next big showcase of upcoming Switch titles will be at E3 2017. Nintendo has detailed its plans for for the show and it includes a Nintendo Direct-like stream, treehouse events, and tournaments. You can find out more about Nintendo's E3 2017 plans here.