In ssh I can force the IP version with ssh -4 or ssh -6. Is it possible to do the same with sshfs (if yes, how)? When I try sshfs -6 it doesn't work and I see this error fuse: unknown option -6.
fuse: unknown option -6
You can use -o to specify an option, and in particular this one to replace the default ssh command:
execute CMD instead of 'ssh'
So, basically: sshfs -o ssh_command="ssh -6" ...
sshfs -o ssh_command="ssh -6" ...