We currently have 3 different AAD tenants, but we would like to have one company associate directory which combines all those tenants into one so we can search for associates across all of the tenants. This isn't possible in SharePoint People search since it only pulls from the tenant the SharePoint site is connected to. Any suggestions?
The only solution currently is to "sync" objects between the different tenants, either via scripts or third-party tools. That said, Microsoft is working on addressing such scenarios for the overall tenant-to-tenant migration problem, and one of the features we should be getting in the (not so near) future will be cross-tenant people search.