What was Sergeant-at-arms Kevin Vickers’ choice of firepower to shoot down a terrorist, you ask? Check it and see.
I would give long odds that it was a Smith and Wesson 5946 in 9mm. They come with 15 round magazines. I doubt that the RCMP used the politically correct 10 rounders.
The 3953, above, is also issued, but it is more likely he had the 5946.
The picture is from a discussion of the RCMP pistols on defensivecarry.com.
Another source confirms that the Smith is the choice of the RCMP. From Silvercore Firerams Training, BC(pdf):
Smith & Wesson 5946 – The Side Arm of the RCMP
Manufactured 1990 – 1999 A double-action-only (DAO) variant of the 5906, this can be visually distinguished from other models by the complete lack of decocker levers.