Is it better to fish the darker spots between light poles at the canal at night, or is the rock structure more important? I know on a beach at night light scares the cows off, just trying to become more productive.

A constant light like at the canal generally does not spook the fish.

hooker,,, use the lites to your advantages fish the dark edge of the shadows... more important is location, w/ timing of the tide .... and time spent on the canal..... go fishing...

The lights don't bother the fish one bit, especially if you're jigging. And when plugging, as stiffy mentioned, they can actually help. Shadow lines are natural ambush points. And FWIW, the white lights make better shadows than the yellow ones ;)

Knowing the bottom structure and when a spot produces on what stage of the tide are much more crucial.