Been a while since I took a road test or read the book, but I'm pretty sure you cannot change lanes in an intersection.
I had to look this up a couple of years ago and couldn't find anything in the HTA that specified that the act is in fact illegal. I consulted with a police officer friend of mine that confirmed changing lanes in an intersection is not against the HTA. It may very well be unsafe, and not a practice to get to comfortable with, but not illegal. Personally, I won't do it unless it is absolutely necessary.
This is the most I found today about passing. Sorry, I don't have the time to dig any deeper.
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. R.S.O. 1990, c. H.8, s. 148.
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.
R.S.O. 1990, c. H.8, s. 149.
Passing to right of vehicle
150. (1) The driver of a vehicle may overtake and pass to the right of another vehicle only where the movement can be made in safety and,
(a) the vehicle overtaken is making or about to make a left turn or its driver has signaled his or her intention to make a left turn;
(b) is made on a highway with unobstructed pavement of sufficient width for two or more lines of vehicles in each direction; or
(c) is made on a highway designated for the use of one-way traffic only. According to section 150, paragraph (1), subsection (a)...we may pass to the right of a vehicle that is making a left turn.