DO NOT TAKE A BUS!!!
I did it, twice, because like you I didn't want to drive, and will never do that again. As GBiD noted, at the border, the bus will be pulled over to it's own special area. Your bus will need to wait it's turn to be inspected. Everyone has to get off, with all your luggage, you can not leave anything on board or underneath, and go into a building where each person goes through the usual questions. If the agents have any issue, with any passenger, you are stuck there until either the issue is resolved, or the border agent releases the bus without the person that goes in the back for additional questioning.
What would normally take about 3 minutes by car (being questioned once I reached the customs booth), took me 45 minutes going into Canada, 3 hours going back into the US.