Your company has two divisions named Contoso East and Contoso West.

In SC-300, Microsoft emphasizes Azure AD B2B collaboration for cross-tenant access without extra Microsoft 365 licensing. The guidance explains that organizations can invite external users as guests to their tenant to access Microsoft 365 resources such as SharePoint Online and Teams, and guest access does not require an additional Microsoft 365 license for the guest. The host tenant remains licensed for the workloads being accessed, and Azure AD billing for B2B collaboration is handled through External Identities (MAU) if configured. The study content also notes that synchronizing a single on-premises AD forest to multiple Azure AD tenants is not a supported topology with a single Azure AD Connect server, and deploying another AAD Connect to sync the same identities to a second tenant introduces complexity and is unnecessary when the requirement is simply to let users in one tenant access resources in another. Application Proxy (publishing on-prem apps) is unrelated to granting SharePoint Online cross-tenant access. Therefore, the minimum-effort, license-compliant approach is to invite Contoso East users as B2B guests in the Contoso West tenant and assign them the required SharePoint permissions.