Couple of years back we decided to visit NY via Montreal and take the train through the Appalachians - and return the same way.
Should have been a wonderful trip - we had our (paid for and organised on line) appropriate entry forms for both countries ready.
At the border south the train was halted and every pax had to go in turn to a compartment where two officials were installed and answer just about all the same questions (all over again in our case) and spend about 15 minutes or more doing so. The forms were ignored (that’s only for entry by air...) Train was held up for over 2 hours to enter USA. They beat that on the return journey where we had 31/2 hours delay to enter Canada.
Screwed all arrangements for those two days. I guess this happens on a daily basis?