Tableau recognizes only the first three characters of the six-character Canadian postal code - the forward sortation area. If Canadian postal codes in your data are formatted with all six characters, you can create a calculation to map the postal codes. 

If all your postal codes are Canadian

The below instructions are based on the attached canadian_postal_codes.twbx

1. Select Analysis > Create Calculated Field 
2. Name the field Postal Code, enter the following formula, then click OK: 
   LEFT([Customer Postcode], 3)
3. In Dimensions, right-click Postal Code and select Geographic Role > ZIP Code/Postcode. 
4. Drag Postal Code to Detail. 

You will now see a mark for each three-character postal code in your data. 

If your data contains both US and Canadian postal codes 

The below instructions are based on the attached multiple_countries_postcodes.twbx. 

1. Ensure that your data source has a column for country names. In this example, the field is called Country. 
2. Select Analysis>Create Calculated Field 
3. Name the field Postal Code, enter the following formula, then click OK:
   IF [Country] = "Canada"
THEN LEFT ([Customer Postcode], 3)
ELSE [Customer Postcode]
END
4. Drag Postal Code to Detail. 
5. If not all postal codes appear and # unknown appears in the lower right hand corner of the viz, you might need to edit their locations. For more information, see Edit Locations. 

To voice your support for the future implementation of the feature for supporting 6 digit Canadian Postal Code, please vote for the Idea.