You want to establish a dedicated connection to Google that can access Cloud SQL via a public IP address and that does not require a third-party…

When established, Direct Peering provides a direct path from your on-premises network to Google

services, including Google Cloud products that can be exposed through one or more public IP

addresses. Traffic from Google's network to your on-premises network also takes that direct path,

including traffic from VPC networks in your projects. Google Cloud customers must request that

direct egress pricing be enabled for each of their projects after they have established Direct Peering

with Google. For more information, see Pricing.

Reference: https://cloud.google.com/interconnect/docs/how-to/direct-peering