although i can't tell you which information is more accurate, i too saw 744 as aircraft for your flight.
I don't understand why you would get downgraded though as I don't think the 77W CX uses for that route is the 77G (J only) as it looks as they're only using that config for YYZ. But maybe they're going to switch the YVR route as well. i sure hope not since we're booked on CX889 early oct in F and i will be incredibly pissed off if we don't get F.
don't forget that 77W is CX's terminology and refers to all of their 777ER 300 planes and although i'm not 100% sure, they all have F.
If indeed it is a 744 then you should get F.
If by any chance it turns out to be a 77G, then maybe you could get on the 889 flight. I would ask them to change you for free if they can't provide the class you booked originally.