LXD doesn’t provide any CPU load avg information, so you would need to pull that data in yourself and create containers based on your own metrics / judgements. (LXCFS can now provide per container load avgs)
From the LXD side its probably much easier to do a round robin approach as CPU load avgs can change pretty quick (i know you have 1/5/15 minute load avgs but that doesn’t mean loads don’t spike) so it can be hard to analyse and judge where is best to deploy a container.
For example if I have an LXD host dedicated to running cron jobs once an hour and I looked at the load avgs it would be quite low, so I think great and deploy a web server to it, once an hour when the cron jobs cause a spike its possible it could cause the web server to drastically slow down / be non-responsive (a pretty unlikely scenario but you get the idea)