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Does anyone know if quarantine should be done at our final destination or it can be done at the POE?!

My POE will be Toronto and my final destination is Winnipeg. I intend to quarantine in Toronto and after those 14 days do a road trip to Winnipeg. Is it feasible?!
I don't think so. You need to check with Immigration. Also, when you will come to Winnipeg you need to quarantine for 14 days as per current rules.
 
Yes. I don't have a TRV, and their response was that I don't need an Authorization letter.
I only have an expired COPR (expired in May)

If you are coming to Canada to reunite with your immediate family members with an expired COPR, you can travel if the airlines allows and you have no exit control from the country you are travelling from.
 
If you are coming to Canada to reunite with your immediate family members with an expired COPR, you can travel if the airlines allows and you have no exit control from the country you are travelling from.

What! How will border control process an expired COPR? Won't they deny entry?