First of all, a cluster of two Proxmox nodes won't work. They are based on majority voting, so if one node goes down, the other one fences itself. You are better off using three nodes, and if that's not possible, you need a third device that is configured as Qdevice.
Then, there is no cluster-aware file system that works as well with shared block storage like you know with VMFS. You only have only two options: LVM (non-thin) or ZFS-over-iSCSI. Both have their downsides, for example LVM doesn't support Snapshots.