You can use Istio for this already, where one cluster is the master: https://istio.io/pt-br/docs/setup/install/multicluster/share... I've never tried across cloud providers, and so I don't know if latency would be a factor, but I think in theory it could work.
You can also join clusters with Istio just for admin and network traffic, i.e. one cluster with Istio in Azure and another cluster with Istio in AWS, talking via the mesh infrastructure. https://istio.io/pt-br/docs/setup/install/multicluster/gatew...