Plastic weld the shell. Replace the handle.

For the shell: Yes, you can fix a crack in a roto-molded cooler with plastic welding.
For the handle: I wouldn’t bother – just replace it.

Epoxy or JB Weld looks like a quick fix, but it won’t flex with the plastic and will fail under temperature changes or a heavy cooler. Plastic welding actually bonds the material back together. Get a soldering iron (or a dedicated plastic welder) and some zip ties – the zip ties act as filler rod because they’re the same polyethylene. Melt the crack edges, fill with melted zip tie, smooth it out. It’s ugly but strong.

Handles are a different beast. The hinge points take all the weight and constant movement. Even a good plastic weld will fatigue and snap again. Best bet: drill out the