Automatically start service on WSL on Windows:

First configure it to start the service without asking a password.

Create line in /etc/sudoers.d/ (at WSL to prevent asking password):

%sudo   ALL=(ALL) NOPASSWD: /usr/sbin/service xrdp *

Create .bat file in Windows startup directory with for example the following lines:

wsl sudo service dbus start

wsl sudo service xrdp start