all i can say is that trying to fit a friends airsoft rail onto my real sl8 worked except for the 2nd screw hole lining up, which could be drilled to work. i imagine this is how they get away with legally saying "parts will not fit a real gun".
your best bet would be to ask the seller to measure center to center between those 2 rear bolt holes, and then check your sl8. as i say, the difference i saw was about 1/4" and a properly placed hole could be drilled into the gun to line up if one isnt worried about drilling on there gun.
or, you could see about getting one of these to canada.... still a very nice price in the states
http://www.hkparts.net/shop/pc/G36-SL8-Full-Low-Profile-Picatinny-Rail-187p1514.htm
but good luck with THOSE extra costs.
the airsoft stuff (grip, rail, stock) WILL fit with a bit of touching up with a file here and there to the airsoft piece and a bit of fooling. is it worth it?
it depends whats more of a headache.... paying to get the real parts to canada at 10x the cost, or some fudging and knowing you have airsoft parts on your expensive gun.
in my opinion, for the prices, it would almost be worth the experiment alone.
not to mention, ive seen some high quality airsoft parts made in aluminum that are still only made in plastic by HK.
im sounding like an advocate for airsoft parts, but over all, the quality i have seen is almost matched with the real thing at WAY lower prices and easy availability.
unless your a name brand whore.... some are.
perhaps this should become another thread as i feel like im hacking this one with blasphemy. i know there are many out there that would disagree with my thinking.
