On this, I have flown both 767-200 and -300 along with A330 / A340 on the YYZ - YVR route many times in the last 18 months. I find that I aim for flights with the Airbus aircraft, mostly because the aairplane itself is newer and more comfortable. Air Canada's 767 aircraft are getting a bit long in the tooth, and the ex CP aircraft are in many cases in definiate need of refurbishing.
Both aircraft are well layed out in Y with 2+3+2 and 2+4+2 layout, much nicer than the 777 with its 2+5+2 or 3+3+3 layout (IMHO). I also try to upgrade to J, and find that while AC's 767 aircraft may have 1+2+2 (give me the 1 anyday!), the Airbuses have much nicer overall accomidations up front.
I usually fly the WB Airbuses because they are newer, hence less worn out. I have yet to fly one of the new Air Canada 767s, so I will hold judegement on them.
As for looks, while the A340 is a nice looking plane, the 767-200 in origional AC paint is one of my all time favs!
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Photo © Michel Tougas