Google Cloud Platform has made hybrid- and multi-cloud computing a reality through Anthos which is an open application modernization platform. How does Anthos work for distributed data platforms?
For example, I have my data in Teradata On-premise, AWS Redshift and Azure Snowflake. Can Anthos joins all datasets and allow users to query or perform reporting with low latency? What is the equivalent of GCP Anthos in AWS and Azure?
Your question is wide. Anthos is designed for managing and distributing container accross several K8S cluster.
For a simpler view, imagine this: you have the Anthos master, and its direct node are K8S masters. If you ask Anthos Master to deploy a pod on AWS for example. Anthos master forward the query to K8S master deployed on EKS, and your pod is deployed on AWS.
Now, rethink your question: what about the data? Nothing magic, if your data are shared across several clusters you have to federate them with a system designed for this. It's quite similar than with only one cluster and with data on different node.
Anyway, you point here the real next challenge of multi-cloud/hybrid deployment. Solutions will emerge from this empty space.
Finally your last point: Azure and AWS equivalent. There isn't.
The newest Azure ARC seems to be light: it only allow to manage VM out of Azure Platform with an agent on it. Nothing as manageable as Anthos. for example: You have 3 VM on GCP and you manage them with Azure ARC. You deployed on each an NGINX and you want to set up a loadbalancer in from of your 3 VM. I don't catch how you can do this with Azure ARC. With Anthos, it's simply a service exposition of K8S -> The Loadbalancer will be deployed according with the cloud platform implementation.
About AWS, outpost is an hardware solution: you have to buy AWS specific hardware and to plug it in your OnPrem infrastructure. Need more investment on prem in your move to cloud strategy? Hard to convince. And not compliant with other cloud provider. BUT ReInvent is coming next month. Maybe an outsider?