Amazon FSx for Windows File Server is the correct choice because it is specifically designed to support Windows-based file storage requirements, including the SMB protocol, and can be accessed from multiple sites. Amazon EFS is designed for Linux-based systems and would not be suitable for a legacy application that requires a Windows-based file system. Amazon S3 is object storage, not a file system, and does not support the SMB protocol natively. Amazon FSx for Lustre is optimized for high-performance computing workloads, not for Windows-based file systems.