If the goal of the logo is to grow a brand and draw tourism, then why would you want to use a bland complex such as the city hall as the centerpiece of the logo? Yes city hall is important for Toronto, but it's not exactly like the White House to international visitors. Tourists are drawn to the CN Tower, the islands, the tall buildings, Chinatown, etc. Fun things. The best logo in my opinion would be the skyline. It's globally recognizable as one of the best. The silhouette used on this site makes for a much better logo than city hall does. At least if your goal is to draw international visitors.
All that said, Toronto doesn't do bad for tourism, considering that in 2011 it drew $5 billion, vs $7 billion in LA.