The attack started at the Canadian War Memorial.
If we are smart, we will issue ammo to the guard at the Tomb of the Unknown Soldier and put a few extra armed soldiers discreetly around the immediate grounds. I can easily see jihadis taking the opportunity to try and murder the guard and blow up the Tomb.
We should too. The honour guards carry unloaded rifles and are not issued ammo because the post is considered ceremonial, not operational.