Ok I'm heading out Sept 27-30 and staying in Bellevue and possibly going to Canada. It's my first time going my boyfriend and I love to explore but we aren't so sure if we should just use public transportation (I heard it's great).
Hey Kimberly! It really depends where you want to go in Canada and what you want to do. If your plan is to mainly visit Vancouver you can take the Amtrak train from downtown Seattle to downtown Vancouver. It's easy, fast and beautiful! If you have the time and want to explore more then renting a car would be better.
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Rent a car-- no question. Bellevue is a pale shadow of interestingness compared to Seattle and it isn't close to downtown Seattle at all. 20+ minutes from Bellevue to Seattle assuming no traffic (and a bridge toll if you take 520!). Also, Bellevue isn't remotely walkable unless you are right downtown.
Alternatively, Car2Go and Uber are great options for as-you-need quick transportation. Way cheaper than a cab and likely in the neighborhood of a rental car with less check-in-check-out fuss-- you could bus into Seattle (and take the https://www.boltbus.com/ or train to Vancouver).