Gun laws do not stop shoootings any more than "Wild West" right-to-bear arms culture prevents shootings.  Unbalanced individuals, religious or ideological fanatics are everywhere and can acquire weapons. The dead shooter was known to the authorities.
The armed Sargeant-at-Arms did take down the armed intruder in the Parliament Buildings, so he did his duty without some armed citizen needed. 
Don't know all the details yet as to whether there was more than one shooter or if the dead one killed the War Memorial Guard soldier.
Most illegal weapons in Canada cross the border from the US, where there are no gun laws.  *** 

I don't agree that this is our 911; totally different; besides we were involved in 911, from many Canadians killed in the Towers to cooperation with air travel (taking airplanes that could not enter American airspace.)   But it may be an eye-opener to naive Canadians that what happened today is a common occurrence in most of the world. We're not in Kansas anymore, Pollyanna.

Edited to add 911 statement