TORONTO—Canada is pulling out all the stops to make sure the world's leaders are safe this weekend at the Group of Eight and Group of 20 summits the country is hosting.

For the city of Toronto, the hub for both meetings, that has meant turning downtown into a veritable fortress for much of the week preceding the June 25-27 events, complete with hurricane fencing, shuttered banks and boarded-up sculptures. Downtown businesses urged employees to stay away or work from home over the past few days.

There...