Given the diagram above, a Salesforce org, middleware, and Historical Data store exist with connectivity...

When designing a solution to view large volumes of archived data (over 20 million records) without physically storing them back in Salesforce, a Data Virtualization pattern is the architecturally preferred approach. This pattern allows users to view and interact with external data in real-time without the overhead of data replication, which would otherwise consume significant storage and impact platform performance.

To maximize declarative configuration, the Salesforce Platform Integration Architect should recommend Salesforce Connect. Salesforce Connect allows for the creation of External Objects, which behave much like standard objects but point to data residing outside of Salesforce. This is achieved by having the middleware (ESB) expose the Historical Data store via an OData (Open Data Protocol) endpoint. Once configured, call center agents can view historical case items directly on the Case record page using standard related lists or lookups, all configured through the point-and-click interface rather than custom code.

The provided landscape diagram illustrates a clear path from Salesforce through middleware to the Historical Data Store. Option A leverages this by using the ESB to bridge the protocol gap. Because the data store is already "fine-tuned to be performant with search queries," Salesforce Connect can efficiently query only the specific historical records needed for the current case view.

In contrast, Option B requires a "Request and Reply" pattern using Apex callouts and custom Lightning components. While functional, this is a code-heavy approach that increases technical debt and does not meet the "maximize declarative configuration" requirement. Option C, using "Fire and Forget" with Platform Events, is unsuitable for a synchronous "view data" request; Platform Events are asynchronous and would require a complex, custom-built UI to "wait" for and display the response. Therefore, the combination of OData and Salesforce Connect provides the most seamless, scalable, and low-maintenance solution for call center agents.