We can use PeerDB to replicate each node (worker and coordinator) from one Citus cluster to corresponding nodes in another Citus cluster. It will require some customization, and I am happy to assist you through the process. Also, just as a heads up, prior to PeerDB, I worked at Citus for 8 years as an early (solutions) engineer, so I have a pretty good understanding of Citus internals. :)
If not, then is there any other solution?