Definitely something to be aware of the possibility of occurring, but there's nothing preventing insurgent/Taliban/Al Qaeda forces from acquiring US, British, or any multitude of uniforms of allied nations (whose uniforms are readily available through surplus stores, ebay, internet, etc.) serving beside the Canadians in Afghanistan and carrying out an attack as described.
It's been done by insurgent forces in Iraq during fighting in Fallujah and Najaf and achieved limited/little success (The insurgents didn't use the uniforms for suicide bombings, but rather in the pitched street battles to try and infiltrate into American lines).
I'd be more worried about an attack of multiple VBIEDs used to breach and attack a facility, ie. Palestine Hotel in Baghdad than a single footborne suicide bomber disguising himself as a Canadian in cadpat clothing and equipment. Also, a lone soldier attempting to enter a compound or infiltrate a body of troops would draw attention unto himself, as it's very unlikely that a single troop would be 'outside the wire'. Then when he's challenged/questioned by the gate guard, unless he spoke perfect english or french (depending on the working language of the unit deployed) it'd become very quickly apparent, something was fishy and the situation would be handled accordingly. Proper force protection requires some sort of id check/challenge procedure for persons entering friendly lines, no matter how they're dressed or what sort of vehicle they're in.
Outside of the wire suicide bombers have got ample opportunity to get into lethal blast range of patrols without having to 'Cadpat' themselves up.
If there were a legitimate fear of being infiltrated by insurgents/terrorists dressed in cadpat uniforms and equipment, I'd be more worried about the Pakistani knock-off cadpat stuff done by Parklands being used for an infiltration attack, seeing as how the stuff is readily available in Al Qaeda's own backyard.