I have had mine open on the highway - slight wind noise - but I would say you really don't need a deflector. I had one on my VUE and it seem like it made more noise with it than without it.
The rear passanger one has no noise when open! LOL - :drunk: ;D
As I have stated before, the Enclave have a built in Deflector at the very front of the opening. It keeps wind from blowing into the cabin and cuts down on the noise. I don't have the Enclave yet :banghead: but I have an STS with a similar Sunroof and at 80 MPH I can talk in a normal voice with it open.
Open the Sunroof and you should be able to push the Deflector down. It's spring loaded and should pop back up when you remove your hand. 8)