Ahh, sorry, didn't think about that one. Our only child is still in the rearward facing position, so we haven't had to use the center "over the back of the seat" latch yet. My suspicion is that there isn't one in the center, but I'm not sure. Of course, a lot of older cars with early latch systems don't have the center latch either, so I guess it isn't out of the question to still place the seat in the center without that connection. Probably not the absolute gold standard of safety, but if you needed to do that short term for some reason it might be perfectly safe anyway.
There are some services that will install a baby seat for you... I've never used them before. Not sure if it is the local police, fire dept., or someone else. If you find out there isn't a center latch, then ask around, find out who does that in your city/town, and take it to them when you get your Enclave. Tell them you'd like to place the seat in the center and see what they tell you re safety etc.