Tenant connection is chosen by setting the persistence unit in the query. While something automated could be used to do reflection-based lookups, it would be unreliable. An object can belong to multiple persistence units, meaning that some sort of logic would need to be added to manage which is "best-match" and allow for overrides. Sometimes simple is best.
Logic was implemented in a way that would not impact existing default connections. This makes use of the Quarkus default label in the code, along with an available override when using only named units.