Hi Leandro,
The details you mentioned here is SAP CTR specific and you don't need to map mandant as the nature of CTR is support multi mandant information.
Also the external view you are creating may already exist on TDF system (not on source ECC). Run this query to see a list of external views on the system:
SELECT * FROM SYNONYMS WHERE SCHEMA_NAME = 'SAPNWH';
Regards, Fernando Da Rós