Finally, everything seems to be clear and fall in one complete picture.
Immediate family members of Canadian citizens and PRs are exempt from travel restriction (regardless their status, e.g., CoPR approved after March 18 etc.), as long as they have valid travel and relationship documents, AND their travel is considered essentials (E.g. establishing full-time residence in Canada) they are allowed to enter Canada. I also called CBSA agent today to confirm this.
I just got off the phone with a CBSA agent about the same exact question, and she told me the opposite. She said that since my fiance's permanent residency application is processing but has not yet been approved, he would not be able to come with me to Canada on a visitor visa, even though our intention is to establish full-time residence. She said that is not considered essential.