Is it possible to trace a wire to a breaker if you don't have access to the inner copper
Yes, a professional tracer tool that has either an inductive feature or an inductive clamp will work. The inductive feature is used by placing the tool in close proximity to the wire, while the inductive clamp is typically an accessory that you place around the wire you're tracing to insert the signal. It doesn't matter if the circuit is energized or not. Unfortunately these tools are expensive, so you might want to find someone you can borrow from or a tool center you can rent it from. People that would have access to these tools would be ones that work with or around underground utilities, so for example I know an excavator that has one of these. Other uses for these tools are finding underground irrigation and breaks in invisible dog fence wires if that helps your search.

Ideal makes one for about $1200:
https://www.idealind.com/ideal-electrical/us/en/products/test-measurement/circuit-tracers/suretrace-circuit-tracer-61-959.aspx

Schonstedt also makes a few different ones that would work:
https://www.schonstedt.com/

And here is an instruction manual on how to use the Schonstedt features:
http://gfretwell.com/electrical/howtofindcablemanual_06.pdf