Airborne radar is not limited to the Catalina, which is, btw, a big, slow target. It'd never be able to keep up with the bombers. But, if there's ever a water SAR option, it would certainly be cool.
The H2S radar element on bombers was used quite a bit, not for air-to-air, but rather, air-to-ground. These were carried on Stirlings and Halifaxes as Pathfinders, which we don't have. The US did use B-24s and B-17s as foul-weather lead-bombadier missions, but I don't think it was before 1945.
Air to air sets like the British AI MkIII to MkVIII sets were carried on Blenhiems, Beaufighters and Mossies, but they were strictly used for night interception.
To be fair, if you used a radar equipped aircraft as a defense measure...then its only reasonable to have aircraft with those counter-measures. German night fighters used a Naxos radar detection set to home in the H2S Pathfinders, the Brits used a device called Serrate to track German signals in the same fashion.
Either way - implemented or not, the development and usage of radar-equipped a/c in WW2 has always been one of my favorite topics.
J