I am heading to Vancouver next March, via a couple of days in Seoul on the way through.

A mix of airlines with Air Canada doing the pacific leg is about $900. Korean Airlines all the way through are $1200. Korean have bigger seats ad a bit more legroom according to seatguru.

Has anyone flow both and/or can comment on whether Korean are worth the extra?

I have done both, Korean Airlines is superior. The stewardesses are prettier, AC's reminded me of linebackers, the food and service are better and I am sure the safety is equal. I avoid Chinese airlines when I can, once on a flight from Guangzhou to Vancouver, an Aussie drank his dutyfree and terrorized the plane until a lumberjack Canadian put one of them down with a punch. The man was hogtied and stayed that way until Vancouver airport when the Mounties boarded and removed him in cuffs. I also imagine the little Korean women know hop ki do and would have kicked his ass.

Korean Air is one of the best airlines and they give you Kimchi.
Never took Air Canada but most ratings on the net rank it quite low ...

Haven't used either but I know Air Canada has a terrible reputation.

Done both, quite a few times. Definitely more attractive stewardesses on Korean Airlines, but, that's true of pretty much all Asian airlines vs western. Discrimination laws and all that...

Remember also that Air Canada is a Star Alliance member - so, going with them, there is a chance you'll actually find yourself on an Air China flight disguised as Air Canada. Now, I haven't flown on a Chinese airline in quite a few years... But I find mainland Chinese to be quite awful to fly with. Horror stories of spoiled grandchildren whose whose grandparents keep feeding the kid sugar snacks jumping up and down for 12 hours straight... Or so much piss on the bathroom floor you could use it as an attitude indicator for the flight come to mind.

Then the big oooooooooohhhhhh and ahhhhhhhh once the mainlanders see the coast of BC and are overwhelmed by the beauty, everyone getting up from their seats and crowding around the windows with their phones and cameras. It can be quite a sight in the right weather, but still... it's annoying.

Unless the $300 is a big deal, I've got to agree with the other posters - go Korean Airlines.

As mentioned, Korean is better. Nicer planes is the clincher for me, though hot stewardesses is also a bonus.