Comment 2 for bug 1782221

It appears that the .netdev file can accept the MAC address value:

[NetDev]
Name=br0
Kind=bridge
MACAddress=01:23:45:67:89:AB

If you specify the macaddress in your yaml, this should work:

network:
  version: 2
  renderer: networkd
  ethernets:
    ens3:
      match:
        name: ens3
  bridges:
    br0:
      macaddress: 00:11:22:33:44:55
      interfaces: [ens3]
      dhcp4: true

The renderer of the netplan.yaml likely knows this information and can provide it.