I'd have to disagree
being a good route for any potential march on Ottawa
. The symbolism of the GG and her role is great, but three and a half kilometres is quite a walk for a crowd. (And what of those of us who mildly resent the role of the monarchy in our modern polity, and long only for the Liberal caucus to not act as if it were above the law, custom and very spirit of representative government?) Plus, if there were to turn out to be any sizable numbers, I'm guessing police barricades would be set up in similar locations as last year's visit from President Bush - which means Parliament Hill would effectively cut off from Lowertown and points beyond in Rockcliffe by the most direct route, forcing a significant detour, even if it was just Rideau blocked off to Dalhousie again.
Besides, Parliament Hill is traditional. It's where protests happen for even matters under provincial jurisdiction (banning pit bulls, say) or even mostly unrelated to the federal government at all (q.v. demonstrations for ejecting Syrian troops from Lebanon
); it's a high-visibility location, with easy media access. Rideau Hall is a bit of a fragile and ceremonial location, but not the Centre Block lawn; it's our version of the original Speakers' Corner, and accepted as such. Straying elsewhere is just asking to be ignored.
But, then, hopefully we won't have to find out, right?