96 Legacy GT wagon 2.5.

 

What's the black plastic canister between the ABS pump and the upper radiator hose, with the vacuum hoses sticking out?

I'm guessing from here it's the charcoal canister.

^ yep.'the charcoal in it absorbs any fuel vapor smells, etc, so you dont get gas smells inside the car.

Evaporative emissions canister. It's to catch fuel vapor from the gas tank rather than letting it escape into the atmosphere and cause global warm... I mean, climate change.

 

The engine sucks the vapors out when driving and burns them away.