If there are multiple network devices reporting flow data to Cascade and two devices report flow
records for the same TCP connection, what will Cascade report? 

The traffic will be double counted. 

Cascade will discard one of the flow records. 

If both flows types are the same (e.g. NetFlow) Cascade will de-duplicate the records but if they are of different flow types, one record will be discarded. 

Cascade will de-duplicate and consolidate the flow records regardless of source and flow type. 

This is not possible.