>>Can I use WebRTC to call H323?
Yes. You can. WebRTC can uses any standard signalling protocol capable of exchanging SDP.
To use H323 you need the following 2 things
1. Java Script library implementing H232 protocol that will run in the browser.
2. H323 Signalling Server(gatekeepers) which can communicate with Java Script library by websocket or using other mechanism like BOSH
So far I know there is no such server[2] or JavaScript library[1] available now. ( either free or commercial )
If you don't have the requirements to support legacy device supporting H323, It is not a good choice to use H323
You can use SIP or XMPP.
You can easily build an Asterisk Server to support SIP via websocket and use sipml5 as a client and call bot SIP and H323 endpoint.
If you like to test only then I think signalling using nodejs will be most easy approach.
Thanks.