You can pass on both a single or a double yellow line in Ontario.
The Ontario Traffic Manual sets the guidelines for when a single or double yellow line are to be used. Basically a double yellow is used when it is likely to be unsafe to pass, such as going around a blind curve. Single yellow lines are where it also may be unsafe, such as approaching an intersection or on parts of a 2-lane road, etc. They're guidelines only, basically telling you that it might be unsafe to pass in that area. What's really important are sections 148 and 149 of the Highway Traffic Act. 148 deals with overtaking and passing rules. Here's the important part of that:
Quote:
Passing vehicle going in same direction
(8 ) No person in charge of a vehicle shall pass or attempt to pass another vehicle going in the same direction on a highway unless the roadway,
(a) in front of and to the left of the vehicle to be passed is safely free from approaching traffic; and
(b) to the left of the vehicle passing or attempting to pass is safely free from overtaking traffic.
And section 149...
Quote:
Driving to left of centre prohibited under certain conditions - 149.
(1) No vehicle shall be driven or operated to the left of the centre of a roadway designed for one or more lines of traffic in each direction,
(a) when approaching the crest of a grade or upon a curve in the roadway or within 30 metres of a bridge, viaduct or tunnel where the driver’s view is obstructed within that distance so as to create a potential hazard in the event another vehicle might approach from the opposite direction; or
(b) when approaching within 30 metres of a level railway crossing.
Exception
(2) Subsection (1) does not apply,
(a) on a highway divided into clearly marked lanes where there are more such lanes for traffic in one direction than in the other direction;
(b) to a road service vehicle where precautions are taken to eliminate the hazard; or
(c) on a highway while it is designated for the use of one-way traffic.
Nothing about single or double lines. Section 150 deals with passing on the right. As long as you haven't broken one of the above rules, and you pass in safety, you're okay to pass on a single OR double yellow line.