Very difficult call.

Both are fantastic places. Vancouver has scenery around and you can take a day driving to Whistler and back along the Sea to Sky highway which is truly magnificent.

OTOH, Seattle is also lovely with the Experience Music Project, Pike Place Market and if you want to be sad, Boeing Factory Tours.

My dining recommendation for Vancouver is Al Porto. Great food at very reasonable prices. My favourite in Seattle is Salty's which offers great seafood.

The good news is, whichever one you choose, you won't go wrong.