Originally Posted by astroflyer

Just to try to provide a little more detail and confirmation.
1) Don't fill out the US customs form. The pre-clearance section is now all GE machines, and it's to the left of the customs hall (separate entrance). They do like to see a physical card when you enter.

2) From all of my experience, Nexus has always been open when US customs was open. This includes some stupidly early flights.

3) As was mentioned before, you do have to fill out the Canadian customs declaration. Nexus kiosks are located both to the far left and far right of the customs hall.