Using expedia to book flights, in comparison with direct air Canada booking, also means that you need to talk to the third party for any changes. Air Canada does not make any changes for any Expedia tickets, if you call AC, and they ask you to talk to the broker Expedia to make changes. For the last two years, the customer service in Expedia has plummeted rapidly, must worse than directly dealing with individual airlines.

My practice is that if I find the fares at Expedia are more attractive than airlines, AND I do not expect any changes in my travels, I book via Expedia. Otherwise, I book directly through airlines websites.

Similarly for hotels, I look and compare. Many hotel bookings at Expedia do lose frequent guest program points.