Hi,
Over the Internet connection, do you mean some layer 2 tunneling protocol over Internet?
Please also note the requirement for latency:
"latency shall not exceed more than 100ms between the two devices. Exceeding this latency can cause the cluster to go into an unstable state, with effects varying from dual mastership and or the inability pass traffic."
You could have 2 control links & 1 fabric link, with 1 control and 1 fabric on same L2 physical network and the other control on another L2 network.
Is it a branch or High-End SRX?
Cheers,
Ashvin