I would look closely at the exact flights that were offered on ITA matrix, that they are in CAD, and the you have checked the box to only check flights with seats available. As we are heading the same way the same time as you, I did a quick check from YEG and it came up with a $315 return flight to LAX, but in looking much closer, the plane stopped in Toronto. (that was a looonnngg out of the way travelling just to head south). Direct to LAX is showing $415 CAD, and that is the same on WJ site as well. You can copy the matrix booking info into a bookwithmatrix website, and then see if you can still get the cheap seats.
TA's don't normally have access ti flights cheaper that you or I could get, they sell the seats at the Airlines price, and get their money from selling you the extras, Hotel commission, insurance sales, ticket sales, etc.