I recently booked a flight with Malaysia Airlines. The price on Expedia for TD would have been double (!) the price I had to pay on the airline's website. And this was a very simple, one segment, nonstop, oneway flight within Malaysia, for 2 people.
And as the airline's website charges in a different currency than CAD, Expedia's best price guarantee does not apply.
Also: Last Winter I drove across Canada. I found tons of smaller Canadian hotels/motels showing as fully booked on Expedia for TD, but they had plenty of rooms available over the phone (or their respective websites, if any). In fact, most of these establishments were almost entirely empty, which wasn't surprising, given the season.