Thanks again for all the tips.

I ordered the Chinook Book and it came quickly. It has 2 coupons, one for a "buy one, get one" adult fare and one for a free child with paid adult.

The former was only good on the northbound leg for some reason, and the child ticket good one-way so I got to use both and saved $69.

I made the mistake of going in person to Homewood to use the coupons and buy the tickets. That Amtrak computerized ticketing system is seriously antiquated. It took almost 1.5 hours to accomplish everything; things were not helped by the fact that the agent misspelled all three of our names even though I wrote them out for her (and she swapped mine with my son's so I had a child's ticket) and had to re-ticket everything a couple times (I figure for a cross-border trip the names better match the passports exactly).

The agent was also not aware for a while that to buy the tickets I had to produce our passport numbers and the dates of expiration. Or at least that's what seemed to be required for the tickets to print.

Anyway, it was a real learning experience and several people behind me were seriously inconvenienced.