I wanna study study aerospace in future in m.tech now in b.tech which branches I should choice electrical , electronics , mechanical

You can do M.Tech with introductory scale degree in Electrical, Electronics or Mechanical. Still grounded on experience. Better you opt for mechanical engineering at the undergraduation stage to have better understanding of subjects.

Aeronautical and Aerospace Engineering are interdisciplinary branches. You can do M.Tech with basic graduation degree in Electrical, Electronics or Mechanical. However based on experience I will recommdnd you to opt for Mechanical engineering at grad stage to have better understanding of subjects