Might be worth edging your bets on either Ngannou TKO or Gane via decision. I think we can all agree we don't realistically see Ngannou winning via anything else, and Gane probably has a slim chance of knocking out Ngannou.
From what I understand it seems Ngannou is interested in re-signing with the UFC but wants a clause in his contract that allows him to box as well. Dana should probably compromise and give it to him or allow him to do it and get a 10% cut of the fight or something. It would be a huge loss for the UFC if he leaves and more more fighters will end up going when they know they can get get huge sums for these super-star cross-promotion boxing fights. Connor got an exception with Mayweather so it's not impossible. That was a co-promotion with the UFC and I believe Dana got quite a hefty cut of McGregor's purse so it's probably something he should consider letting some of the other UFC superstars do, otherwise he risks losing them all together.
Personally, I wish fighters weren't held ransom by Dana as much. They shouldn't be restricted in participating in a different sport to MMA, I get that Dana doesn't want fighters moving to another organisation, while still contracted to the UFC. I get that, but the only reason they'd do that is because of money, so make it worth their while, so they wouldn't have too.
Obviously, you'll get those that are just out there to make as much money as possible, so I get the idea of limiting it to other organisations, but to boxing? I don't think so. Maybe, Dana could potentially restrict it to signing on a multiple contract basis, but allow them to fight the one of fight every so often. It doesn't hurt Dana, and if a UFC fighter does well in boxing it could potentially bring in new fans to the UFC.
Now, I know that Ngannou looks a bit underdogish for this fight, but I bet on him because, firstly, I like to bet on the underdog, you get high multipliers, and, secondly, in my personal opinion, Ngannou's chance of winning is above 50%.
From an outcome perspective, I'd say Gane has a chance of submission, and points with a outside chance of knocking him out. While Ngannou has a chance of knockout, potentially a very slim chance of a submission. So, I'd say that purely from a outcome perspective Gane has the better probability because of his tools at his disposal. However, we know the power of Ngannou, but we also know the movement of Gane.
This is probably one of the hardest to call fights in the heavyweight division for some time. Completely opposite fighters, but you can never really rule out a power hitting such as Ngannou.