Interface to ClearScada

We have a water industry customer with a number of legacy SCADA/Historians/RTUs etc across around 30 sites.
We are doing a Proof Of Concept that will hopefully replace these systems
One stumbling block is that a some sites have ClearScada connected to DNP3 devices and/or Radtel RTUS (with proprietary protocol)
So our options are to develop Radtel interface (undesirable) or connect to the ClearScada System at these sites.

Has anyone have any experience and/or advice on how we may go about connecting to ClearScada?

Thanks in advance