I shall be travelling to the US and Canada this month, and have a query about US customs. We are British citizens both with ESTAs, so are eligible for VWP, this question is not about visa requirements. We are travelling to Canada via Newark airport with an overnight stopover on the outward leg of the journey. This stopover is at one of the airport hotels. On our return journey, we fly back to Newark and the are staying in New York City for a few days. When entering the US on our outward leg do we need to tick the box for transit or visitor? And, on our return journey will we need to pass US customs again as if it were an entirely new visit? Or, if we enter the first time as a visitor will it be counted as a single trip?
On your outbound trip through Newark, since you will be entering on the VWP, any tick box you might find for "transit" or "visitor" has no practical consequence and is probably for statistical purposes only. (The CBP Traveler Entry Form does not appear to have such a "transit/visitor" tick box.)
You will definitely need to pass through US customs again on your return trip from Canada - there is no shortcut.
Note that if you plan to spend close to 90 days in Canada, you will need to consider the rules of the VWP for such visitors. From Visa Waiver Program:
If you are admitted to the United States under the VWP, you may take a short trip to Canada, Mexico, or a nearby island and generally be readmitted to the United States under the VWP for the remainder of the original 90 days granted upon your initial arrival in the United States. Therefore, the length of time of your total stay, including the short trip, must be 90 days or less.
This means that after your first entry to the US under the VWP, your 90 day maximum US visit clock does not stop until you leave North America.