C. Give Super User permission to the partner manager users: In Salesforce Communities, particularly within the Partner Community, the Super User access allows designated partner users to have greater visibility into data owned by their partner organization. Specifically, it lets them view and edit data owned by other users within the same account (distributor in this context), even if the organization-wide defaults are set to Private. This approach meets the requirement by enabling partner managers to access all Case and Container records owned by their peers without granting them unnecessary access to partner executive data or data from other distributors. It's a scalable solution because it leverages existing Salesforce functionality without the need for custom development or maintenance-intensive sharing rules.

The correct answer is C