There is no general air defence these days. There are point installations protecting military targets, on military land, but there aren't batteries of missiles to defend large cities. If needed they launch intercept aircraft. (imho those military point defence installations are turned off most all of the time. See below.)

Recently in Vancouver we hosted the woman's world cup. Joe Biden was in town. And so was this (http://i.imgur.com/pvxYN49.jpg). That's the USS Stockdale entering Vancouver port to provide him cover. It left port the day after he left town. All very quiet. Local news didn't speak of this big thing coming in unescorted. I only noticed after one of our boats went screaming by the dog beach (http://i.imgur.com/G7lY9s4.jpg) about half an hour before. It was probably leaving to make room at the dock. When the Stockdale left it was followed by a tug and a rib from the local cops... they probably learned about it at the same time I did.

Stockdale's itinerary listing it docking in North Vancouver. http://www.uscarriers.net/ddg106history.htm

The lack of air defence is probably a good thing. The error rate, the risk of shooting down something by accident, would be unacceptable.