Not sure where this crack came from, but it looks like it could be from hauling in wind, which I’ve done plenty recently. Any reason to worry about this? Any repair advice? I was thinking of sanding and recoating the bottom, but I’m not familiar with Gelcoat.
Easy for me to say, because it isn't my canoe, but that doesn't look particularly problematic. If you really wanted to, you could cut a fillet into the crack and fill it with gel coat or thick epoxy.
If it's just a scratch in clear gel coat and not a crack in the laminate that compromises structure, I'd probably just leave it alone. Trying to apply a matching clear gel coat or a clear epoxy may end up looking messier than the scratch.
You can probably hide most of the scratch cosmetically by wiping on (and then off) some Flood Penetrol and then some 303 Protectant.