If GCP have fedramp high that’s roughly equivalent to AWS govcloud (fedramp high ~= IL4).
AWS and Azure also have IL6 regions (able to hold secret information).
Finally AWS runs a top secret cloud for the intelligence community. I believe Azure announced a similar project but not when it’ll be open for business.
Unlike AWS and Azure, Google doesn't offer any GovCloud regions, only Fedramp which seems to apply to unclassified data only.