You want to establish a dedicated connection to Google that can access Cloud SQL via...

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.