My most recent experience with Air Canada...
My wife and I booked tickets from Calgary to Toronto.  We just went basic economy, no extras.  Although we booked and paid for the tickets (1 1/2 months ahead) with the same last name and contact information, and same booking number, at the same time, they didn't put my wife and I together on the plane.  However, for an extra $100 (one way), we could select seats set aside so we can sit together.  Really!  I phoned and complained and was told "that is now happening all the time, and there is nothing I can do about it".  Outrageous!  Why doesn't Rovinescu park his behind where I sit? 
And just to prove it wasn't a fluke, the same thing happened on our return flight.  Talk about a one digit salute to their customers. 
Unfortunately, WestJet is little better.  Last flight, we booked months ahead, had an 8pm flight from Toronto, and they bumped us to a 10pm flight with no notice (until we checked in 24 hours ahead), and no apology.