Alex, while a fantastic fighter, doesn't exactly look untouchable in most of his match-ups. Gane is a massive, quick dude with good footwork and shot selection who would be able to go tit-for-tat with him in a lot of striking exchanges. Furthermore, Ciryl has a lot of experience fighting kickboxers and making them look silly.
Don't get me wrong, Pereira's accolades shit all over Gane's and I also believe that Poatan is a superior striker on a P4P basis to guys like Volkov, Rozenstruik, Tuivasa, etc. But Ciryl has so much margin for error given the size disparity. He has shot for takedowns and hunted submissions in the past and is still sharpening that particular weapon. While Poatan's defensive grappling has largely held up, it's still a work-in-progress and asking it to perform just as well against even larger dudes is a big ask... especially since Gane doesn't even have to take him down per se. His clinch game alone is quite punishing and he could use that to make up ground in the distance striking should he start losing at range.
I would be interested to see how Ciryl handles Alex's calf kicks, admittedly. Those could be very effective at hampering Gane's footwork especially given his open stance. That said, Ciryl is no stranger to having guys go after his legs. Even putting aside his Muay Thai background, Volkov came in heavy with low kicks against him in Round 1. Gane by his own admission hadn't trained to prepare for that and assumed Drago would target his body instead. So after dropping the first round, Gane went back to his corner, made adjustments, and came back out to totally outhustle Volkov after that. Tuivasa has the most dangerous calf kicks at HW and also tried to target Gane's legs; Ciryl defended & countered them and Tai pretty much stopped committing to them after that. I would expect Alex to have a little more success given his utter lack of telegraph mixed with his power... but I'm not sure it would be enough.
I think Pereira would have a legitimate chance to make something happen, but I'd favor Gane in the fight.