Booking hotels on Expedia means that you can potentially lose out on points when you directly book on sites like Marriott.com. However, is there any negatives to booking Air Canada flights on Expedia vs directly on the Air Canada website?

I am using Expedia for Air Canada flights to get the additional Expedia rewards points, and the only negatives right now I see are that I don't get all the seat selections that I would get if I used the Air Canada website. Are there any other losses in terms of points redemption or other negatives?

Note that Expedia doesn't have booking / change fees.

Thx!