managed k8s services like EKS and GKE provide cloud native CNIS.
https://docs.aws.amazon.com/eks/latest/userguide/pod-networking.html https://cloud.google.com/kubernetes-engine/docs/concepts/alias-ips
we can install also deploy service mesh like istio provided CNI in the cluster https://istio.io/latest/docs/setup/additional-setup/cni/
Now As part of the Istio installation, if we deploy Istio CNI along with VPC native CNI how would the cluster network behave since both CNI's are running in parallel inside the cluster.
The Istio CNI plugin actually runs as a chained CNI plugin, which means it is added to the configuration of the existing CNI plugin configured for your cluster. It should work fine with most CNI plugins.