Why doesn't Canada build nuclear weapons already?!?

Once America runs out of their resources or their economy collapses, or some other tragedy happens, who's to stop them from invading Canada and stealing our resources (fresh water, oil, etc.)? Who or what can deter them? Nuclear weapons, and Canada needs them. We have the capability to build them and to drop them on their major cities if they declare war, so why don't we? Only a fool would believe that the U.S will be honorable if it needs something Canada has.