Red, you can take Amtrak (train) between Seattle and Vancouver. Crossing the Canadian border to the US in a rental car can be a real pain in the butt, and while it is a short flight, the train ride is about 4 hours, and that's from downtown Vancouver to downtown Seattle. Getting through US preclearance in Vancouver airport adds an hour or so to your day, so it's probably a wash between flying and train.

Fro the flight, Air Canada does have a non-stop to Vancouver. No one has a non-stop to Seattle from Sydney, so you would need to connect in San Francisco or Los Angeles. Not a huge deal, but price each option out. Do not connect in the US to fly to Vancouver, since then you have to go through US Immigration and Customs, then do it again in Canada.