Assuming that bird has advertised the prefix and now those IPs are routed to your LXD host, then you have a choice of how to use those public IPs in your containers:
If you don’t want to allocate the entire subnet to LXD, and instead want to use individual static IPs, then take a look at the routed NIC type lxc config device add <container> eth0 nic nictype=routed ipv4.address=194.50.X.1 that adds static routes to the host for you automatically and doesn’t need an additional bridge. See https://linuxcontainers.org/lxd/docs/master/instances#nictype-routed