S3 is newly strongly consistent within a single region since last reinvent or so (google cloud storage has been strongly consistent for much longer). However, the cross-region replication for s3 is based on 'copying' [1] so presumably async and not strongly consistent.

GCP datastore and firestore are strongly consistent nosql databases that are available in multi-region configurations [2].

[1] https://docs.aws.amazon.com/AmazonS3/latest/dev/replication.... [2] https://cloud.google.com/datastore/docs/locations

S3 became strongly consistent only recently (https://aws.amazon.com/blogs/aws/amazon-s3-update-strong-rea...) while I think GCS and Azure Blob Storage has strong read-after-write consistency for a while now.

In any case, Cloud Spanner provides strong consistency in multi-region deployments.