G7 s have been run at a resort outside Huntsville, ON with similar ease of security. From a practical point of view that's the sort of place where these shindigs should be held. The G20 meetings are bigger and thus need to be held in bigger centres but even then there are better options than putting them right downtown, the city and province wanted the Toronto G20 to be held at the CNE grounds but Harper overruled them leading to the disaster there.