Neither Virtualization or Clustering is a method to use additional resources from other hardware. A virtual machine is hosted on a single physical server - but can then be moved to another physical server if needed.

Clustering is a secondary physical server that is available if the primary node fails. The secondary server cannot be used at the same time for the same instance of SQL Server.

You can use the second node in a cluster for additional instances - but those instances would share the resources on that single node.