When booking a ticket to/from Canada on Amtrak's website, you are asked to provide passport details for all traveling passengers. In case you don't know the exact details at booking time, can you put in "Unknown" in all the missing fields? Or are those details verified at the bus/train station?
From personal experience (round trip from Vancouver to Seattle), the answer is no, those details are not verified. In fact, nobody even bothers to verify the names on the ticket. You do have to show a passport with a valid visa when you arrive at the station, but those details are not matched with whatever you typed in at reservation time.
The situation is similar to how the passport details treated on flights - nobody cares about them, so you can type in whatever you want.