I can also gaurantee that a Brit flying into Canada and then crossing into the US at any of the bridges into Buffalo will need to stop and get a visa. It is US$6.

We have friends and family that occasionally fly into Toronto and then we pick them up and drive them across the border. If we aren't picking thenm up, I make sure know about the $6 US payment for the visa and even send them the cash to make sure they have it, and the $1 toll for the bridge across Grand Island since they were driving.

Yet you have not actually provided an example of a rail passenger being left at the border due to delays in processing paperwork.

Amtrak trains, by federal law, are given priority over freights. Does this always happen in practice? No. But you won't see a train leave for the reason of missing its "slot" (this isn't LGA or DCA we're talking about here). As you note, the train is given 2 hours to cross the border into the US.

I still contend that in the absence of any hard evidence, saying that the train is more likely to "leave without you" than another form of transportation is pure speculation. A two-hour window to clear the train should be sufficient.

The train waits for a long time and is frequently stopped at the border for 3hrs+ (from experience.) Non US/Canadian citizens have to get off. I am pretty sure they wait for everyone to get processed because of the excessive time spent at the border.

The bus (which I have also taken probably close to 100 times) stop is much quicker. Everyone has to get off and go through immigrations/customs both ways. I have seen people get left behind at the border (though I don't know the reason.) The longest delay I have had at the border (delay as in we were waiting for people to get back on the bus, not a delay due to traffic at the border) was about 30 minutes or so. However, buses are a lot more frequent. From Toronto there can be 4 or 5 buses leaving between 7 and 10pm. If you miss one, you can probably take the next.

One thing about fares: the bus (~10h) is CHEAP. If you book in advance, it can be as little as $40 one way. The train is generally around $90+ one way and takes 12-14h. The plane can be as little as $90 one way or as much as $200 depending on the season / day of week etc.

I generally find the bus to be worth the savings. However, the train takes the whole day (no overnight option) and it's not even that cheap. So I either do bus or plane now depending on time constraints.