I have a dataset with Canadian Postal Codes and I'm hoping to use this visualization feature but I'm really struggling to find any sort of documentation in terms of how the districts are coded, can anyone help? Is there a standard district code that RapidMinder uses by default?

i think this map expects the "Official Name Census Divison (English)" if you join by Name.
https://public.opendatasoft.com/explore/dataset/georef-canada-census-division/table/?disjunctive.prov_name_en&disjunctive.cd_name_en&sort=cd_name_en
If you have access to the PCCF you should be able to map the Postalcode to the Census Division.
Greetings,
Jonas