Bill,

I don't believe that the train was actually cancelled, what happened which unfortunately has been happening much of the summer, is that the train was running very late. When that happens, Amtrak chooses to bus people from MSP to Chicago so as to get them there on time and to help preserve connections to eastern trains. If you would not have minded being hours late into Chicago, you probably could have still taken the train when it showed up.

All that said, since you decided not to take their offer of the ontime bus, the only recourse you have is a refund of your original fare. I think it unlikely that Amtrak will do more than that.