Customs is an absurd issue, which could be resolved via pre-clearance and reduced to a 30-min pre-board, with little or no wait at the border....but don't hold your breath waiting for that.
When I took it they brought all of the passengers off the train, then the train went away for a while (30 minutes), then it came back. Is it possible they were using the x-ray scanners normally used for freight on it? Certainly an unique customs experience.
For the individuals crossing, I had very few questions (despite going for 5 months as a young individual). They just reminded me I couldn't work and sent me through. I typically got more questions when going to New York for a weekend.