Yes, first - sleep. Read that other thread that scylla linked to. Get organized first and think about what you have already and what you can pull together. I repeat - my personal view is that you do not need to get on a plane to Canada immediately. (You can certainly write in explanation that in covid you do not wish to travel unnecessarily nor leave without your wife; it's also fine to say that some things you do not have timing on because of the long processing of your app).
These are only my thoughts.
1) Read. Read the other threads. Make notes and get ideas from others as to what they have provided and what you can provide. Post less, read, think a bit.
2) Go over what you submitted already. Look at it with a critical eye. Read the email from them again. Go over what you submitted again. (Any movement or change on any of those things?) What can you provide again to re-emphasize?
3) Write, start to write, explanation. Bullet points. Key points you will make. NOT long explanations. Bullet points. Go over and modify this. Remove things frequently that are not factual. Not much emotion - facts.
Some rough ideas about how to structure, roughly grouped - to answer the questions of intent and how you will live. I mean structure primarily in linking the points you are making to evidence and documents you can provide. They are better at reading lists with supporting documents than long explanations.
-Where will you live? (Supporting evidence - residing with a relative first is fine if that is the plan, or discussions with realtors, etc).
-How will you support yourselves? (Savings, employment, studies, contacts with employers, etc). What will your wife do?
-Cutting ties with current residence: plans to move. Quitting employment, plans to quit employment, supporting letters, etc.
-Intent: supporting letters from family/friends about your discussions with them. Other evidence?
-Logistical planning: bank accounts. Travel plans. Contacts with movers. Etc.
These are only my thoughts. Group your evidence and support. Start with what you have already. Identify things you can obtain and show relatively quickly.
Once you've started to pull this together, again, look at it with a critical eye - what is missing? What holes can be filled? What evidence do you have that is non-factual and can be removed (this does NOT need to be a novel). If there are parts that are missing that you can explain, SHORT brief notes on this (i.e. covid difficulties and do not wish to do excessive travel).
As far as the background (from govt perspective) - you've received some hints from the request (you've spent very little time in Canada). They do not want people to use PR status as a way to have a 'backup residence permission' while continuing to live abroad. That doesn't mean this is an inquisition. You're being given an opportunity to demonstrate your good faith intentions together with your spouse to move permanently to Canada.