May I offer you a warm welcome to the CameraLabs forums.
Well, while Gregory wants to discuss Photoshop
I'll stick to the brief. I've just opened a RAW file in DPP and checked that the lens info was present. I then used the "Convert & Save" function to convert to an Exif-JPEG and then open the JPEG in DPP and the lens name is still present. But if I open either the original RAW or the JPEG in a third party program such as IrfanView the lens name isn't shown which leads me to suspect that this is encoded in manufacturer specific data.
The only differences with my setup here are that I use a 40D (but the EXIF data should be encoded the same way) and that I use the latest version of DPP (188.8.131.52 for Windows). I'm not aware that the problem you describe was an issue with 3.4 and fixed with 3.5 but you may want to visit your Canon site and check and download the upgrade. If you do then upgrade all the apps, such as EOS Utility etc., to maintain interoperability.
Please let us know how you get on.