There is no official source for it - even IRCC doesn't even mention what the Calgary office does, it's just a process of deduction:
- Nobody has ever mentioned that their portal emails came from Edmonton. Our group here on this forum is statistically significant so I'm confident in this statement
- People from BC, Alberta, Sask & Manitoba (Western Canada) have always said they got landed from IRCC Calgary
- People in Ontario I believe are getting landed by IRCC Etobicoke
- People in Quebec and the Maritimes are being landed by IRCC Montreal
- Exceptions to this are Whitehorse, which appears to solely deal with RNIP applicants, and Niagara Falls for H&C cases
Unless I missed it, I have never heard of anyone being landed by Edmonton - from what I understand Edmonton is a secondary VO for PR applications and primarily a temporary work permit CPC. It just wouldn't make sense to have two prairie offices for Western Canada landings.