Canon cable release with Nikon D3100?

Would a cable release designed for a Canon camera work with a Nikon?

No. They go to a lot of trouble to make sure the two companies don't work together.

The connector is not the same. Otherwise all cable releases are pretty much the same.

You will have to buy one from Nikon ( if they even sell one for the D3100, I don't know) or get a cheap one off Ebay. A Canon release will be wired exactly opposite, just so it won't work.