Depending on where you live, it is usually cheaper to book thru the cruiseline when having to fly 2 one-ways. Your transfers are included if you are flying in/out the day of the cruise. You can pay a deviation charge and request your own flights, and I would suggest staying in Hawaii a few extra days if you can and flying into Vancouver a day early (especially if you must fly to Seattle and bus to Vancouver). I did the Ensenada to Hawaii route on Celebrity and I think we paid less than $700 for the air, including the deviation form Minnesota. (we paid less for the cruise, though, because we got it for 50% off!) We could not have gotten it cheaper on our own. Frequent Flier tickets don't work because of the open jaw. Celebrity accepted our flight requests and we did not have to pay extra. Sometimes you do. We requested non-stop flights on Northwest. Others cruising with us did not do deviations and they had bad connections on Delta. Made for a miserable day of travel.
Just my opinion. Check it both ways. I believe you are better off accepting the air portion now and you can always cancel it 60 days out if you find a better deal on your own. Otherwise, the air portion from your city maybe sold out and you will be totally out of luck. Deviation charges are non-refundable once you acept their offer.