You can leave Canada the next day. This is just what I did a couple weeks ago. I was given a slightly hard time about it though as they 'recommended' in a kind of stern way that I should stay for at least 14 days following the oath. The presiding clerk ended up having to be called into my registration to clarify that it was up to me.
Also worth noting that the other poster saying that the certificate can be mailed to the US is incorrect, at least from my experience as someone who applied from within Canada right before moving to the US. They refused to mail it to the US and I had to provide a Canadian address. They also said that it couldn't be forwarded by Canada Post. Have a backup Canadian address handy. I'm dealing with how I'm going to get the certificate back to myself in the US now.
One other thing is that they made me show proof on the call that I was physically in Canada since my most recent address was a US one and I (truthfully) told them that I traveled up for the oath the day before. Luckily my hotel room had a view of Niagra Falls and I held my camera up to the window as proof which was accepted lol. Not sure how I would have answered that otherwise though and the question caught me off guard. I would think of an answer ahead of time for that. Maybe keep your travel itinerary handy or an arrive can receipt around in case they ask? Hopefully they're easier on you.
