Hi @mmani99,
Fundamentally, each Canton-based driver/domain has the same privacy and interoperability guarantees. For privacy, in particular, these are that transactions are only distributed to Canton system entities on a need-to-know basis and subtransaction privacy. Thus, in your case, if Alice, Bob, Charlie and David are parties on separate or the same Canton participants, Alice and Bob would not know about the transactions of Charlie and David (and vice versa).
A caveat to the privacy aspect is if a blockchain-based domain is used (Ethereum, Fabric or Corda) and when Alice, Bob, Charlie or David also have access to the underlying blockchain that is used to persist the Domain/Sequencer data. This is analogue to giving read access to the database in a database-based domain. In this case, they would be able to see which on-ledger identities (so not Daml parties) transact with each other. They wouldn’t be able to see the actual transaction itself.
So far, we don’t have plans to support using Tessera for Besu. However, private data collections for Fabric will likely be supported in the future.