Can private flights between the US and Canada avoid using a port of entry?
CANPASS gives a streamlined entry into Canada, allowing you to land at a port of entry and just report by phone.  To go into the US, you need an eAPIS account.  I think that with eAPIS you still need to meet in person with a customs person.  A friend in Montreal used eAPIS to travel to Vermont regularly.  He said it was a lot of hassle to get set up and go through the process the first time, but after that it was not too bad.  On the way back he just had to land at a convenient POE and call in.
Not quite an avoidance of POE requirements, but otherwise pretty convenient.