If you have a photocopy of your passport, you can try giving that to the US embassy. I have no idea if they will accept it. You can't get your actual passport back unless you withdraw your refugee claim and leave Canada. The passport will be handed to you as you are boarding your flight to leave Canada.
Pay for a consult with a good US immigration lawyer to find out your options. Basically you want to know if there's any way to navigate this without being able to give them your passport. If there isn't, then you would need to withdraw your refugee claim in Canada, leave Canada, and then complete the US immigration process from your home country.