VCF All the way...
The product that best meets the requirement for automating the deployment of an active-active datacenter leveraging a vSAN Stretched Cluster with the least administrative efforts is:
C. VMware Cloud Foundation.
VMware Cloud Foundation (VCF) provides a unified SDDC (Software-Defined Data Center) platform for the hybrid cloud, integrating vSphere, vSAN, NSX, and vRealize Suite into a single platform for consistent infrastructure and operations. It includes automation capabilities for deploying and managing the entire stack, including vSAN Stretched Clusters, which helps streamline the deployment process and reduces administrative efforts.
While vRealize Automation (option B) and vRealize Orchestrator (option D) are automation tools that can be used for deploying and orchestrating various components, VMware Cloud Foundation is specifically designed to simplify the deployment and management of the entire SDDC stack, making it the most suitable choice for this scenario.