It can't be "missing copper". The composition of the 1906 cents was an alloy of 95% copper, 4% tin, 1% zinc. No Canadian cents were clad or plated until the late 1990's I believe. There's a line on your coin where you can see the metal has been eroded away.
That coin saw a lot of action and cleaning and bad guck, I mean bad luck, over the years. The edge discolouring looks like a bit of salt corrosion, common on the streets of Canada in the winters, or any other corrosive material it could have come in contact with in the last 100 years.