The CRN is automatically generated in the Global eTrade Services system based on your inputs of the date and flight number using the following criteria mandated by the CBSA:

The Conveyance Reference Number (CRN) consists of the Flight Number and the date of departure (YYMMDD).

E.g. If flight XX123 is departing to Canada on December 4, 2013, the flight number would be XX123131204.