POET Technologies Inc.

Regarding the restrictions on shorting. It is true that you can only sell short using your unregistered (eg. "margin" or "cash") account. Regulation rules prohibit you to do that on registered (eg. RRSP, LIRA, TFSA) accounts. And this is regardless what broker you use.

But I don't think it makes the shares you have on those accounts unavailable for other shorters to borrow.