Ship docks at 6 in Vancouver but people might not get off until 7 or later. When I was going on the Hawaii cruise that left Vancouver. We were going to breakfast and we were like where is the ship. Than we seen the ship coming. It arrived maybe 8 or later I forget the time. 10 is way way too early for me. Even flying out of Vancouver. You will never make it.
You probably won't be cleared to disembark before 7. If you self carry, you should be fine. You'll be going the opposite direction of most traffic. Seattle can have long security lines so that could be an issue.
You're also going to want to see what events and festivals might be going on.
Just to get from the freeway to the port there can take ages. If you don't hit the freeway then you're battling downtown traffic. Which is all the worse if there's an event going on.
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