I'm a Pulumi user myself, and I haven't seen a Pulumi provider for Incus yet. Once I get further into my Incus experiments, if someone hasn't made an Incus provider yet, I'll probably go through the TF provider conversion process.
I just tried and it seems to have worked (though I haven't tested any specific resources yet):
$ pulumi package add terraform-provider lxc/incus
Meanwhile, running Incus inside GCP VM(s) should be possible, though I haven't tried it and can't confirm it. Incus can manage system containers - containers that behave like VMs running full distros, except for the kernel.
But keep in mind that Incus is more like docker than docker-compose. You will need a different tool to provision and configure all those containers over Incus's API (docker-compose does this for application containers over the docker API). As mentioned before, that could be Terraform/OpenTofu, cloud-init and Ansible. Or you could even write a script to do it over the API. I have done this using Python.