● You must contact the Customs Agent at the port of entry you choose to enter. Also it is a good idea to obtain his/her badge number if there is a dispute on arrival.
● In theory you are required to arrive within +/- 15 minutes of your expected arrival. There are certainly instances where being outside this window can cause significant grief. It is best to adhere to this time line unless your Customs agent specifies otherwise.
● You must taxi to and park in the area designated for Customs. Do not leave your aircraft until told to by the Customs Official. You will be required to provide your Passport and your passengers Passports. You should carry all documents that you would be requird to carry in Canada. Pilots license/medical, proof of registration/ownership, weight and balance, restricted radiotelephone licence, Radio License for your aircrafts radio(s) and proof of insurance.
● On Departure of the United States you must again file an EAPIS Departure submission. Again you will receive an email clearing you to leave.
This all seems to be quite onerous however this is the price we must pay for transborder operations these days. Once cleared by Customs you are free to wander about the United States and enjoy all of the air traffic services you need for your travels. I have found them to be very friendly/helpful. The weather briefers are quite helpful but you must be aware that the briefer may be many states away from your location. Below are links to the various sites mentioned above to register with EAPIS, DTOPS, and telephone numbers for Ports of Entry. The Cross Border Operations Manual is an extensive review of this process.
Returning to Canada is considerably simpler. Again you must file a cross border flight plan. Call CANPASS (1-800-CANPASS) and tell the Customs Agent your port of entry. If you are a CANPASS registrant you will have considerably more options for arrival ports. When you arrive at your port of entry and park in the designated area call CANPASS again. They will either send out Agents to clear customs or give you a clearance number to put in your logbook. Then you are on your way.
I'm Canadian Do I Need to be ADS-B Equipped? - Link to BC General Aviation Association Website