That’s not click and call as normally understood. Although I’ve never used WebRTC, I believe it is a WebRTC call from the browser. To Asterisk there is one incoming call leg and one outgoing one.
As far as I know it is not sensible and probably not possible to do a click to call scenario to a browser, but if you could the channel parameter in the originate, would be the address of the browser based WebRTC client, and the num parameter would be your extension 2000.
Although I haven’t validated it in detail, this topic seems to be about what you actually want to do:
Be warned that WebRTC is a moving target. You should make sure you have the latest versions at both ends (e.g. it would be unwise to try to continue to use chan_sip with it). You should be prepared to have to read up on protocol and do low level debugging.