At this moment we have three rescued Cav's. We had four but one passed from the breeds inherent heart problems. Since the rescue's we have were for the most part, not socialized well, barking has at times been excessive under certain circumstances. They do tend to bark at other dogs but can be calmed quickly by quieting them or if possible, introducing them to the other dogs.
I will say this, when we had all four of them, all from different backgrounds, they were the best behaved, wonderful and friendly lap dogs one could ever want.(for a pack of doggies) We're big advocates of the breed even though losing one to CHF was heart breaking. Good luck with your bundle of Joy!