Comment 3 for bug 1890113

You should be able to add the LXD cluster as a cloud to the existing controller; see the help for "add-cloud":

    juju add-cloud --controller mycontroller mycloud --credential mycred

As to what physical machine the containers get created on, that would have to be inferred from the LXD server to MAAS node relationship.

It's a little fiddly, which is why I think the first option is better.

There is an unanswered question about from my previous comment regarding what benefit clustering affords in this set-up. An answer for that might help us with the best path forward.