It should be noted that Postgres releases their own native ODBC driver to connect, you don't have to use CData's driver.
It can be found on their official release page here:
One of the trickiest and most time-consuming things about using PolyBase with Eternal Tables that use ODBC is data types and creating the External Table schema.
I discovered an easy trick to have SQL give you baseline data types without you having to code it by hand.
CREATE EXTERNAL TABLE [YourSchema].[YourTable_dummy] ( [dummy] INT ) WITH ( LOCATION = 'your_external_schema.your_external_table', DATA_SOURCE = your_data_source ); -- generate detected fields list
It will then give you the schema in the Messages tab which you can use to copy/paste the columns and data types.