This is the command
sshfs [email protected]:/remote/path /local/path/ -o IdentityFile=/path/to/key
Added reconnect to keep connection alive
sshfs [email protected]:/remote/folder /local/folder -o IdentityFile=/ssh/key/file,reconnect
Refer – https://unix.stackexchange.com/questions/61567/how-to-specify-key-in-sshfs