Using GCP interconnect with Bucket (Cloud Storage API)

You can use Shared VPC for this purpose:

Shared VPC allows an organization to connect resources from multiple projects to a common Virtual Private Cloud (VPC) network, so that they can communicate with each other securely and efficiently using internal IPs from that network.

Another approach would be to use VPC Network Peering:

VPC Network Peering enables you to connect VPC networks so that workloads in different VPC networks can communicate internally. Traffic stays within Google's network and doesn't traverse the public internet.

Which one will work better depends heavily on specifics of the project, you can find useful comparison of these two here.