Create a peering connection between VPC1 and VPC2.
On the data center side, create a route. The destination of the route is the VPC2 CIDR block (such as 10.5.0.0/16) and the next hop is the VPN tunnel. Set Extra Network of the VPN tunnel to the VPC2 CIDR block (10.5.0.0/16).
Create a route for VPC1. The destination of the route is the VPC2 CIDR block (10.5.0.0/16) and the next hop is the peering connection between VPC1 and VPC2. (Currently, when you create a peering connection, a route pointing to the CIDR block of the peer VPC is automatically created. You can determine whether to skip this step based on actual situation.)
Create a route for VPC2. The destination of the route is the data center CIDR block (such as 10.3.0.0/16), and the next hop is the peering connection between VPC1 and VPC2.
Create a route for VPC1. The destination of the route is the data center CIDR block (such as 10.3.0.0/16), and the next hop is the VPN tunnel.