FYI, the US immigration at land crossings don't use ESTA (or didn't when I crossed to the US late last year). They said that is only applicable to flying (and from what I have heard, possibly by boat). You still filled in the green visa waiver, and handed over your $6 in US cash only! They sometimes ask for proof that you are retunring (I am a Canadian resident, which seems good enough for them, my parents have always taken copies of their return flight to the UK with them tho).

They do use ESTA at the airport, even when flying YYZ - US so make sure that is done.

Buses and trains do leave people behind if it is taking too long! But normally they leave enough time for everyone to get processed and the immigration guys put bus passengers ahead of cars (which sucks if you get there just before a bus!)