Dfyjkt

I've purchased a bus ticket from Amtrak to go from Vancouver to Seattle and the booking page displayed a warning about special conditions for passengers crossing the border:

Passengers traveling from Vancouver, BC, to the United States should arrive at least one hour prior to departure for border crossing processing.

However I presume that this warning only applies to trains, as buses only go through border control at the actual border, rather than at the train station. But the Amtrak page fails to mention the check-in times for their bus anywhere on their website and likewise my ticket doesn't. Where can I locate this information?

In the end it was sufficient to arrive 10 minutes in advance. In fact it's better not to arrive early as the bus won't open the door until 15 minutes before departure.

On the way back (Seattle to Vancouver) it is likewise sufficient to arrive 10 minutes before departure, whether you're taking the bus or the train. The only time when you need to arrive at least 30 minutes in advance is when you take the train from Vancouver to Seattle, as the passport control is at the train station.

I've taken both the Amtrak Cascades and the Amtrak bus from Vancouver to Seattle many times before.

When going from Vancouver, BC to Seattle customs inspection actually happens at the border for both bus and rail. It is only when coming from Seattle to Vancouver, BC does rail have inspection at the station.

The reason why you're requsted to arrive early is so that an operator can ensure that you have everythingyou need to cross the border (mainly a passport). This helps prevent delays at the border, and the possability of having to leave somebody behind.