This circuit is a dedicated light circuit with 7 can lights. I removed all the bulbs, turned the switch on, breaker trips. I swapped the switch, breaker trips. I' guessing there's a short circuit somewhere but how to go about locating it? The can light wiring is in the attic near the eaves, not easy to access. Is there a way to test the can lights from below or just suck it up and low crawl to each fixture? Once I'm there, how to test?
If you didn't test the wiring periodically as you installed it, it is now for you to do.
I would sever off lamps 4-7 at the lamp 3 junction, relight, see if the problem clears. Then divide the remaining area-of-uncertainty in half and repeat, in half again repeat. Now you are down to 1 light, it is that light or the one before.
If it helps, get some 3/4" plywood and lay it across the joists so you have a roadway and don't put your foot through the ceiling.