The "leaks", if you want to call them that, were true after all and Assassin's Creed III Remastered will indeed be releasing on the Switch later this year.
After being listed on Ubisoft's official website earlier this week, the Switch version of Assassin's Creed III Remastered was made official during the day's Nintendo Direct. Like its PS4, Xbox One, and PC counterparts, the Switch iteration will boast the same combination of the base game of AC3 and that of the spin-off, Assassin's Creed Liberation. All DLC originally released for AC3 will be included as well.
The only major difference for the Switch version of Assassin's Creed III Remastered is that of the release date. Instead of releasing next month on March 29 with the PS4, Xbox One, and PC platforms, the game will be landing on Switch just a bit later. May 21 will be the release date for Assassin's Creed III Remastered instead on Nintendo's platform, which is only about 6 weeks or so after the former so the wait shouldn't be too bad for those looking to play here instead.
Lastly, there's a new trailer for the Switch version of Assassin's Creed III Remastered attached below if you'd like to check it out.