This. So much.
Seattle used to be the big dog in the 90s and early 00s with the explosion of culture and business from there (Starbucks, Grunge, Microsoft, Amazon, etc) but Vancouver has not usurped it since the late 2000's and 2010's brought us all that Chinese money. Sure it's way too expensive due to this, but it's such an international class city now. It's close to 50% asian demographic. I felt more at home when feeling home sick in Hong Kong than I did in any other North American city. And the best thing is everything is brand new due to the huge development in the late 00s. Plus you get all the benefits of Canada - healthcare, people, government, etc.
Here are the only issues Vancouver has in my opinion:
- No Uber
- Cost
- Not much of a nightlife
- The weather between Oct to Apr is awful and dreary (but same as Seattle)
- No real extensive culture history (it's a new city really - or new to being an international city)
That's all. Everything else is incredible here. I've lived in 4 different cities (Vancouver, Boston, San Fran, and Tokyo) and stayed in several other cities for more than 4 weeks (Hong Kong, Seoul, Chicago, New York, Los Angeles, etc) and Vancouver during spring and summer is the best city in the world to live in.
My only caveat is you really need to be a traveller to consider it the best city to live in, as it is missing a decent amount of non-asian culture here - if you want to see things like incredible museums and galleries, enjoy crazy nightlife, see old architecture, etc - this is not the place for that, you need to travel to see that.
But the 2 reasons someone should ever pick Seattle over Vancouver is they A) Can't get a Canadian visa or B) They can't afford Vancouver. Both being very valid reasons.
EDIT - Work opportunities, friends and/or family as well of course.