Looking over your pictures I would say that the back spike is a reproduction due to the shape and number of the small spikes sticking up from the top and bottom of it. There should be 7 small spikes coming up from the top of it and yours looks to have 5 although there maybe one at the end that's snapped off? Regardless of that they don't look long enough and I did think that it might have come from with the Tsukuda or Halcyon Jumbo kits but those are taken from the vintage Kenner version but are slightly smaller (probably due to shrinkage at the moulding stage). It's also off that the underside of it is more black in colour so I wonder if the top was weathered to match the rest of the figure.
I can see though that it is the Canadian version as there's no Coo stamp on the jaw trigger like there is on the US version and the colour of the clear top dome is more honey than smoked gray like the US version. This done does appear to be quite wide at the sides unlike my version but I know these things do change shape over time and no two ones are the same any more. Also, the general colour of your figure is lighter than mine, which is another tell that it's Canadian.
I bought an amazing book recently on this figure called Hideous Plastic which is where all this information comes from and I'm glad i picked it up even though it was quite expensive as it is only available on the Australian Ebay so the shipping stings a bit.
Hope that's of some help and it would be nice to see some more of it when you get the chance.
Ian