FYI, I got a letter from IRCC stating that I am authorized to travel due to family reunification even if I am on open work permit. However when I called CBSA they don't think my trip is essential since I don't have a job waiting for me in Canada, so the family reunification letter became useless after all. I heard from some that open work permit holders are complaining because IRCC modified the rules again about family reunification. If before they mentioned that open work permit holders can travel for family reunification for the health safety and well being of other family members, they basically removed that phrase and some foreign workers took notice of that. Worse part is that they didn't mention of any updates or removal in IRCC website.
Check this link, if you read this text you won't find these details on the IRCC website about family reunification.
https://ibb.co/Fn2yYQP