This match should be interesting.
So, first of all, let's get two of Garou's stuff out of the way. His passive radiations wont work on a Celestial considering that they already resists high level of radiations and, most importantly, they are too big to be affected by them since even assuming a Planet range for his radiations it would still be too little to affect something that is galaxy sized. The same applies for Garou's portals, since he have no feat of being able to create galaxy sized portals.
For AP, I am not sure were Garou scale since his calculation is in joules and I find the values written in tons to be of easier understanding, so I can't express myself on that. Unfortunately there is no proper calculation for where the Celestials scales, but they are Galaxy level because of simply their size, and with their power they were shown to be able to create galaxies or galaxy sized suns in seconds, so they technically should be a bit higher than baseline. But I will say that a calc for them would be helpful, honestly.
And the AP argument is also an interesting one since there is also the problem that Garou doesn't have the AoE/Range to fully affect their body. A punch, for example, in the arm of a Celestials would damage him because of the AP, but considering that, at best, the AoE would be planet size (aka a grain of sand compared to his full body) it wont be able to kill him in a single hit, at least imho obviously.
Now, for the power mimicry, that won't be huge advantage since the Celestials main powers come from their huge size and their Cosmic Energy powers. Assuming that he can copy the Cosmic Energy, that wouldn't make that much of a difference since, as said before, it's that alongside their size and their ridicoulous range that allows them a cosmic level manipulation, on it's own Cosmic Energy wont be of big help as seen with human sized characters that use it, which allows them to just create energy at best and little more.
And the main problem with Garou's skills being used here is, once again, the size of the opponent. As seen with Watchdog Man, he have problems to adapt to fighting style that aren't human-like. The Celestials' huge size will be problematic for Garou before he can eventually adapt to it during the course of the match.
For the Celestials, their main advantage is their huge size and the big Lifting Strenght. Their main wincons would be creating a galaxy-sized Sun, which have enough of a gravitation pull to create a galaxy in seconds, and if Garou gets caught in it he would be killed by both the gravity (since he doesn't have the LS necessary to survive) and the immense heat. They can also create Black Holes to suck him in and kill him with that, and their last main wincon is to just grab him with LS (and considering how big they are they can just close their hand in his general direction and they are more than likely to grab him).
Overall, the main advantage for each are that Garou have the AP necessary to kill them, a huge skill advantage and a powerful RE, but lack the range and AoE to fully affect them, while the Celestials have on their side the size, a big LS advantage and a general range since they can cover entire galaxies with their bodies. I would personally go with a Incon, since either Garou understand that he needs a good hit in the face to kill them or the Celestial create a Sun and kill him with that first, both of which are likely to happen. Though this is just my general opinion on this match, so anyone can disagree with me (and also i think this might be the only comment I make in this since I am not sure of how much time I have to discuss).
