Yes, you can file RTI Applications to Cantonment Board.
Cantonment Boards are Civic Administration Bodies in India under control of the Ministry of Defence. The Board comprises of elected members besides Ex-officio and Nominated Members as per the Cantonments Act, 2006. Cantonment Boards are "Public Authorities" as per Section 2 (h) of the RTI Act 2005.
You can file RTI Application to the respective Cantonment Board by addressing the same to the designated "Public Information Officer (PIO)" either Online or through Post and by paying the prescribed fee.
To know more about the procedure to file RTI Applications online to Central Government Departments, please refer https://onlinerti.com/how-to-file-rti-online-for-center