Is it possible to configure a backup session target on a CUBE? It doesn't look like it, so how do you configure a backup trunk for termination?
Correct, you'll want to create a duplicate dial-peer with the same exact destination-pattern but make sure you have preference 1 configured since the default is preference 0 (the highest). You can then have a different session-target on the second dial-peer for backup. Also make sure to setup a voice class h323 1 for h225 timeout tcp establish 3, assuming it's an H323 dial-peer.
Great reply from Joe (+5), in addition instead of using redundant dial-peers you can create a static SRV record on the GW and have the dial-peer point to that srv record instead.