A Nintendo website once briefly listed The Legend of Zelda: Breath of the Wild for release in March, but Nintendo quickly removed the listing, and they've given no comment on the upcoming game's release date (outside of a generic 2017 window) since then. A handful of sources have suggested that it will be released in June, but GameStop believes otherwise.
During a recent presentation to investors, GameStop noted that Breath of the Wild is one of the titles that's on their "Focused Marketing Calendar" for the first quarter of 2017, or January 1st - March 31st, 2017. Some have suggested that this only means they'll begin marketing the game sometime during that period, but GameStop management later indicated to investors that the properties mentioned on the slide pertain to when a product will be released.
As a major retailer, it's possible that GameStop has some extra insight into Nintendo's release schedule, but they could also very well be speculating. Nintendo, as usual, remains silent.