As far as I know, there is no elegant way to deal with overlapping IP addresses. A second tenant is an interesting approach. If the GCP IPs and the remote office IPs need to talk to the same assets, then keep in mind that the common assets can only exist as managed workloads in one of your tenants. In the other tenant, you'll need to create unmanaged workloads to represent the common assets. I suppose that one set of the overlapping IPs is being NAT'ed somewhere and that will need to be addressed in policy. (The VEN will report the traffic flow as originating from its private IP, but what the destination sees is likely to be a different IP, which could be a single IP or a unique IP for each workload in GCP.)