I think you can, but I am not a Cassandra user, so never tried.
You will have to configure gora.properties (http://svn.apache.org/repos/asf/nutch/tags/release-2.2.1/conf/gora.properties) to enable Cassandra. In Nutch 2 Tutorial (http://wiki.apache.org/nutch/Nutch2Tutorial) the do that for HBase.
To know where is the data mapped in Cassandra you will need to take a look at the mappings at http://svn.apache.org/repos/asf/nutch/tags/release-2.2.1/conf/gora-cassandra-mapping.xml
Nutch will store the data in Cassandra. About Solr I don't know (I never used Solr).