I wanted to rsync and preserve owner and group permissions
rsync -av -o -g ~localuser/ remoteuser@somewhere:~/

but file perms will match remoteuser.

https://askubuntu.com/questions/719439/using-rsync-with-sudo-on-the-destination-machine

edit /etc/sudoers on remote machine adding:
<remoateuser> ALL=NOPASSWD:/usr/bin/rsync

on local machine:
rsync ... --rsync-path="sudo rsync" ...