A bit of a thread resurrection here, but... I am seeing behaviour along the lines of what the OP reported:

1) Google Flights shows three different YHZ-YYZ one-way flights for $471 each this evening. When selected, they all price into Standard. I actually booked one successfully in the past hour through the link to aircanada.com.
2) Searches initiated on aircanada.com show the same flights for $538 each, also in Standard.

What gives?