Hi, is it possible to configure a stack to deploy to two or more providers at the same time? eg GPC, AWS, Azure?

This is an interesting question. Whats the use case?

Yes this is well supported. Just pull in the SDKs for each provider.

I have created templates to pull up resources in three providers, but so far I have to switch stacks if I want to pull up AWS, GCP or Azure. I have thought of calling those templates at the same time without having to change my stack

You shouldn't need to switch stacks, just put all three resources types into the same program.