Please note that CX strictly matches only up to Silver status (except company or targeted status matches) for whatever status (whether its UA 1K or 2P) - although it still offers a good range (priority check-in / boarding / baggage handling and lounge access) of benefits despite being the lowest tier.

BA does not match while AA only gives challenges (for flying AA-coded flights only). CX would be your best choice. They may consider matching to Gold under special circumstances.