Top or Leading integrators for "safe city" video surveillance projects is not a clear descriptor for any level integrator, but I can address largest.
Jason Glover mentioned 2 of the larger integrators, Motorola Solutions and Total Recall which have a presence in the US. I would add Hitachi Data Systems to the list of larger integrators in this space in the US. Hitachi acquired one of the large pure integrators in that space (Avrio RMS Group) ~5 years ago, who were responsible for some large camera deployments in US cities. I would guess there are well over 100 regional or local integrators tackling smaller tier 2 and 3 cities/counties. I can think of nearly a dozen in New York State alone.
In my experience, both as a direct integrator on some smaller safe cities projects, and in talking to some of the larger integrators, the network infrastructure as far as switches, wireless networking, firewalls, are commonly provided by the integrator. Providing WAN physical infrastructure like fiber optics placement will depend on the municipality, whether or not there is existing infrastructure in place (dark fiber).
I would be only guessing that in the really large systems (5,000+ cameras), the budget may exist to add new fiber-optic infrastructure. In the small to medium-sized systems, I have direct experience with, we utilized existing fiber infrastructure where it existed, or installed high-throughput wireless point-to-point bridges instead of fiber.