The LY7 as well as the LLT and LFX were all offered in the CTS. The LLT and LFX are direct injection though, so the injectors for those engines would certainly not work well on a 3.4 DOHC.
For the injectors from the LY7, if the diameters at both ends, fuel pressure requirements, lb-hr ratings, and voltage/resistance requirements are the same, they should work. But I doubt it would be worth the trouble of swapping them. Also, the intake and heads on the High Feature V6es (of which your CTS has), are quite different from the 3.4 setup. The injectors are angled and positioned differently than they are on the 3.4.
I'd say even if you could make them work, it's not really worth the cost/trouble. There are other injectors which do fit, and have been used to provide more fuel to turbo 3.4 DOHC installs, in the past; which are probably cheaper, and certainly easier to install.
The purpose of the twin nozzle is to supply better fuel atomization, not more fuel. My engine is the LY7, but it's my understanding that all of the v6 engines for the 2009 CTS use the same injector. I was just wondering if anyone had looked into doing this.