Yep, GOOlocks usually have Cthulhu, Hastur and Dendar, seeing as Illithids aren't part of the equation when it comes to GOOlocks in D&D.
None of whom are likely to be in BG3. So, it will be some other being associated with the Far Realm. Note that there is no reason to suppose the patron is anything like god-level power, Wyll's patron is only a cambion.
How do you know that? If I play a GOOlock, you bet I want Cthulhu as my patron. But seriously, we don't know yet, which patrons we will get and how they will interact with us.
We know the patrons will appear in person in the game, and we know Larian like to tie everything into the plot, and we know the plot does not involve Cthulhu. Who would have shown up in datamining if his name was so much as mentioned.
