There is no permanent crossover marked outside a school, but a guard is standing in the road holding a stop sign. What has that made the crossing, and what do you owe it?

Correct answer: B. A school crossing — stop and yield the entire width of the roadway until both the children and the guard are safely on the sidewalk

It has made it a school crossing, with the same duty as a crossover. Ontario's guidance defines the term by what is present rather than by what is painted: "a school crossing is any pedestrian crossing where a school crossing guard is present" or where "a school crossing stop sign is displayed." At a school crossing, as at a pedestrian crossover, "drivers including cyclists must stop and yield the entire width of the roadway", and may proceed "only when pedestrians and school crossing guards have crossed and are safely on the sidewalk." That last clause matters: the guard is not finished when the children reach the far kerb, because the guard has to walk back. The contrast is with an ordinary crosswalk, where the full stop-and-yield duty applies only when a school crossing guard is present.

Source: MTO Driver's Handbook: Driving near pedestrian crossovers and school crossings (ontario.ca) — definition of a school crossing