Unlike the Eurostar from London to Paris, is even the Amtrak from?
Yes the passenger rail services are far slower in North America most of them share rails with freight trains. Amtrak owns almost none of its own tracks. As well if you take the train you have to go through passport control at the US Canada border. Same for air and road. But really, most people from Vancouver or Seattle doing a cross border weekend trip will just drive as it is only about a 3 hour trip by car between the two cities. Besides both cities are sufficiently large that a car is handy to have at the far end. So we go by road. Portland is not enough different than Seattle for many Canadians to go farther than Seattle for a weekend trip. But really, Vancouver and Seattle are similar enough that unless therefore is a special event happening at the other city we tend to stay in our own city. You only take the train if you want to see the scenery in between at a leasurely pace.