It used to be sufficient to carry just a drivers license, but now you better also carry a birth certificate or some proof of citizenship. As mentioned above, the problem is getting into the USA, not Canada. I don't know what is going to happen next year when passports or ID cards are going to be required. US citizens will get into Canada, then not be allowed to return home? Will we need to construct refugee camps for all the stranded Americans?
Three years ago I forgot my passport and got into USA with a drivers licence, but not without grief. The agent wanted a second piece of photo ID but rejected everything I showed him. Finally he grabbed my wallet out of my hand a went through the contents. He found an expired AARP membership card, said that is the only one that counts, and let me in. Go figure!
This was on a bicycle trip and we crossed by ferry from Wolfe Island (Kingston Ont) to Cape Vincent NY. Ferries are a great way to cross. We returned across the Thousand Islands bridge and they normally allow bikes on the sidewalk, but not this day because a code orange was declared. However the bridge authority carried us across in a truck and I understand they will always do that when the sidewalk is closed.