If a ship with hot shot cop is attacking Kanan, is Kanan forced to use a focus to trigger his ability? He would satisfy both the "when defending" and "if able" part of hot shot

He is not forced to use it. But using it satisfy HotShot. He may as well is it to modify defence dice (obstructed range 3 comes into mind).

Why so? Kanan ability trigger in step 2 of the flow chart (in the "roll attack dice step"). He would meet hot shot requirements (he's able to spend a token and he's defending).

He's not foced to use his ability. But if he doesn't choose to, he'll have to spend the focus token anyway to modify the 0 eyeballs he most likely rolls. So he might as well.

Why so? Kanan ability trigger in step 2 of the flow chart (in the "roll attack dice step"). He would meet hot shot requirements (he's able to spend a token and he's defending).

But he is not forced to do so as he got other opportunity to do it.

HotShot does not specify WHEN you need to spend it. You just need to spend it sometime during the attack - unless some other ruling - last opportunity is the defense roll not Kanans ability.

it makes sense