While the game will allow you to pick up, and carry, a boat while you are paddling about in a canoe, I was unable to discover a means of dropping the boat. 
 I did attempt to use the new precision placement method in addition to trying to trap the canoe against land and just furiously clicking everywhere but alas, the boat could not be dropped via any means apparent to me.
 I was also unable to leave the canoe, as you would expect, and the only method I had available to regain normal functional play was to relog, which resulted in the destruction of said boat (which I'd permanently borrowed) along with the four beaver corpses inside it.
 Thankfully my beloved canoe survived intact.
 Laughs were had by all. 
 Don't leave your boats unattended people.