NetApp Cloud Volumes Service is the appropriate solution for building applications requiring multi-protocol file access in Google Cloud. It supports both NFS and SMB protocols, which allows seamless integration with both Windows-based and UNIX-based applications. This flexibility makes it ideal for environments that need to handle diverse workloads. The other options like Google Cloud Storage, NetApp Astra, and Google Cloud Spanner do not specifically cater to the need for multi-protocol file access.