The canpass number can be used for advising customs of your intent to land in Canada regardless of whether or not you hold a canpass permit. A canpass permit allows you to land at any number of a list of smaller airports not generally served by customs. You do not need a permit to land at airports normally served by customs.
You do not need to land at the first airport of entry (assuming part 91 here) coming from Canada. The first AOE requirement exists for southern border crossings only. You must contact the customs officers at the airport of intended landing with the details of your arrival. Phone is the best way to do this, an ADCUS message in the remarks section of the flight plan is another.
Ask the customs officer at the AOE in the USA what they expect to be presented with. I think the only REQUIREMENT (part 91) is Form 178 (Private Aircraft Enforcement) and blue declaration cards from everybody on board. Every customs office is different, standardization is not not DHS's forte...