Hi David -
First, there is not currently a method of sending a flight plan (or trip plan) from the iPad to the Garmin Aera 795/795. Given they both have bluetooth, it may be possible to implement as a new feature but I leave any announcement of future capability to Garmin. I would love to see this feature as I do my trip planning at home using the Garmin Pilot App and I have a 795 in my airplane.
Second, unless Apple enables a serial interface for the iPad, the only option would be third party hardware. For example, an iOS app developer could develop a solution where they communicated over bluetooth to an external module which then converted the data to NMEA 0183 sentences and provided a serial connector. This would then connect to an autopilot.
I can not comment on any potential commercial implementation of the above.