Yes, iFly will connect with the Stratus 3. However it needs to be set in "Open ADSB" mode. I thought I heard that iFly had the capability to set that switch appropriately itself. Since it seems it isn't, you need to get an iOS device, download and install the "Stratus Horizon Pro" App. Then, connect to your Stratus 3 with that iDevice and set the "Open ADSB" switch to on/green. Once you've done that, the 740 should both connect and receive data.
As I recall, either way the 740 will connect to the Stratus 3, and it will indicate so in your WiFi page, but it won't gather the ADSB information. None of the boxes will be checked when you access the ADSB Status until after the Stratus 3 is in Open ADSB mode..
The Stratus 3 should stay in Open ADSB mode for as long as no one with ForeFlight accesses your Stratus 3. When ForeFlight connects with the Stratus 3, it automatically turns the switch off.
Also, I believe that only ForeFlight, OR iFly can access the Stratus 3 at one time, they can not both get the ADSB information from the device.