Nanoha official website (http://www.nanoha.com) has announced that the 1st part of Mahou Shoujo Lyrical Nanoha Reflection (魔法少女リリカルなのはReflection) anime movie to be released on July 22, 2017 with total of 90 theaters across Japan. The movie is being made in two parts. Unfortunately, the schedule of the 2nd part has not been revealed.
The three main characters with their voice actors remain the same as the previous.
Takamachi Nanoha (高町なのは) voiced by Tamura Yukari (田村 ゆかり)
Fate Testarossa Harlaown (フェイト・テスタロッサ・ハラオウン) voiced by Mizuki Nana (水樹 奈々)
Yagami Hayate (八神 はやて) voiced by Ueda Kana (植田 佳奈)
The director is Hamana Takayuki (Appleseed XIII). The screenwriter is Tsuzuki Masaki. The character designer is Hashidate Kana (Dog Days’). The anime studio is Seven Arcs Pictures (ViVid Strike!).
Mahou Shoujo Lyrical Nanoha Reflection story was entirely rewritten. The story takes place in the summer after Mahou Shoujo Lyrical Nanoha the Movie 2nd A's ended three months. There's something going on in Uminari city. Nanoha and her group has been commissioned to investigate.
Source: http://animeanime.jp/article/2016/12/29/31968.html