At the moment, it's not possible to use cassandra as a backend for your models (@Model annotation) in Play! 2.0.
There is an effort to provide support for NoSQL Models in Play! via Siena ( http://www.sienaproject.com/index.html ), but the module ( https://github.com/mandubian/play-siena ) is for Play 1.x and cassandra support is not implemented yet.
So, the only way to use Play! 2.0+Kundera is to drop required jars into your lib/ directory, put persistence.xml in META-INF folder anywhere in your classpath (as described in 'Getting started' https://github.com/impetus-opensource/Kundera/wiki/Getting-Started-in-5-minutes), and define your @Entity classes.
However, you won't get support for @Model annotation or CRUD admin area.