Explanation:

The action that an architect should recommend to UC is to configure the main Salesforce org as the identity provider. An identity provider is an application that authenticates users and provides information about them to service providers. A service provider is an application that provides a service to users and relies on an identity provider for authentication. SAML (Security Assertion Markup Language) is an XML-based standard that allows identity providers and service providers to exchange authentication and authorization data. SSO (Single Sign-On) is a feature that allows users to access multiple applications with one login. In this scenario, the main Salesforce org is the identity provider that authenticates users using SAML and provides information about them to the regional Salesforce orgs. The regional Salesforce orgs are the service providers that provide services to users and rely on the main Salesforce org for authentication. This way, users can access the regional Salesforce orgs from the main Salesforce org seamlessly using SSO.