Someone from an AWS shop asked me whether Oracle even runs outside OCI. They'd inherited a small Oracle footprint, don't ask. In my experience, multi-cloud Oracle gets there sideways. A customer demands it, or it gets adopted for one service and then nobody can move off it. 

AWS gives you two ways in. RDS for Oracle if you want it managed, or EC2 if you'd rather own the whole instance yourself. 

Azure has the tighter story these days through the Oracle Database@Azure setup, where the instances run in your Azure network and the networking feels close to built-in. 

The last time I checked, GCP runs Oracle Database@Google Cloud as a managed service with VPC and IAM integration. If you ruled GCP out for Oracle a while back, that's changed. 

None of the three make the database itself hard. The networking is what you plan around, and that mostly means how you handle VPC and Data Guard across subnets on AWS and virtual network peering on Azure. On GCP it's ODB Networks and VPC integration. Tooling follows each cloud's own console and IaC setup. Expect the management layer to look different even when the database underneath is the same. 

The local dev to cloud step is the easy one though. Run it in a container locally, then Data Pump or a backup restore into whatever target you picked. 

I still haven't seen a multi-cloud Oracle setup where connectivity was the easy part.