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Here's the back of the envelope. I am quite curious as to why markings would be of interest?
In the 'good old days', the post offices would often postmark (or "backstamp") every letter that was received to show its progress along the journey, and evidence of when it was received. Here is a random example from
ebay of a nice busy cover that went from Tacoma Washington to Cape Town South Africa (and back) with stops along the way in New York City. You can read the markings and dates to see how long it took during each leg of the trip.

I was hoping that your envelope had a postmark on the back from Hong Kong, and/or one from the destination in Canada, to better document what took place and when.
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There are some numbers at the back and the front. Do they mean anything?
The numbers probably mean something, but not to me. They could be codes from the mail sorter or mail carrier. Maybe the Ø222 relates to the 2Z2 postal code. It looks like the same pen might have been used to write a "G" below the unreadable J7G of the postal code. I don't really know.