Originally Posted by
CKDGM
That's a good answer to a question that isn't the OP's question.
Legally, you're supposed to declare cash both on arrival
and on departure. The OP is asking about the procedure for declaring to the country
that they are leaving (Canada in Toronto, US in Las Vegas).
To answer that question:
CBSA's website says "When departing Canada by air with Can$10,000 or more in your possession, you must report to the CBSA office within the airport, before clearing security." You fill out a form E667 and "Hand the form to a border services officer at the nearest CBSA office that is open at the time you are travelling."
The CBP doesn't have a similarly clear answer on their site, so my advice to the OP is to ask the officer when declaring at YYZ "how do I declare coming back from LAS?" I suspect the answer will be "find the CBP office and declare", similar to the Canadian answer, but I can't say for sure.
Thanks for the answer CKDGM. I kind of knew that much - my real question is where is the physical Canadian office to report to when leaving Canada via YYZ and where is the physical US office to report to when leaving the US via LAS? I've searched high and low and can't actually find an answer to either. I guess as a last resort I could try to phone them and ask where in the airport one needs to report/file paperwork.