I don’t understand how this would make a difference to the level of traffic.
Otherwise, this seems to be almost entirely about the cloud hosting and and the proxy software, not Asterisk/FreePBX.
Although I have no experience of sending anything other than email and web requests to local companies, across the Chinese border, my guess is that you want to use (unencrypted) UDP SIP, with common codecs, direct to the Chinese service provider.