The latest wiki-leaks puts some of this in perspective. Some Chinese officials were discussing how they would be willing to consider a united Korea run by the current South Korea and expect the North to not survive the current leader long. The Chinese were also quoted as expressing severe impatience and frustration with DRK and that they really have little loyalty to it anymore.
While the statement was not intended to be public it is a huge warning to North Korea. I am sure that North Korea has looked at these comments and these alone might temper what they do next.
I am sure that any reunification arrangement would include third parties such as China and the US and would include a treaty that the US withdraw from Korea. With North Korea gone and South Korea satisfied and accepted by China as having authority over the entire country, I am sure the US would have better things to do with its people than to have them there-- especially if their presence was an obstacle. Further the nature of the current military technology means that distance is not a huge impediment and they could withdraw to bases in other places such as Japan and still provide whatever military presence the US would want in the region.
China for its part likely would love to see the end of North Korea, apart from it being a pain it also costs money. The economic arrangements between S. Korea and China are themselves a deterrent and China is much more powerful than it used to be. With the US out of Korea, China would not be concerned about S. Korea as a military threat when Korea's economy would be the first casualty of any hostility.
Put bluntly, North Korea has outlived its usefulness to China and the comments in Wiki-leaks pretty much lay bare that fact.
All this said, I think most of the high cards in North Korea's deck have effectively been removed just from these speculations and comments. I am not sure North Korea is feeling so secure when its only major ally is saying such things.
Another point is that if South Korea ever were to get North Korea and rebuild it-- likely it would be a massive opportunity for Chinese investment and everyone knows it-- China is more willing than most countries to make a massive long-term investment which is what North Korea would need.
Also I think there is widespread understanding that China the US are countries that may be rivals in many respects but they do talk to each other and accidental war is unlikely in that situation since N. Korea talks to China.
The chance of significant conflict in Korea right now-- I'd rate it as pretty low.
Sabre-rattling will continue and low level stuff may happen but I do not expect there to be an out of control situation.
Harper might love the idea of another place to continue his military adventures but he will have to keep looking.
Oh and one more thing-- given the size of South Korea's army and its military capability-- it is laughable that they would turn to Canada which by comparison is insignificant.