Same EAR file isn't automatically mapped to multiple clusters and servers in WAS.
XLD with WAS Plugin
You can map the same EAR to multiple clusters (and servers) and let the WAS plugin create separate applications in WAS for that, each of which is mapped to one cluster (or server). Because the name of that application is the name of the deployed, they will clash by default. You can fix that by putting placeholders in the deployable name and defining container-restricted dictionaries.
Because the name of that application is the name of the deployed.
This solution also allows you update the application per cluster.