Can a Sigma 18-200mm lens be used on a Nikon (originally used on canon)?

Are there lens adapters etc that will allow me to use this lens on my Nikon?

NOPE, not unless you want to shoot in the full manual mode and not be able to shoot with the lens set to infinity.

The distance from the mounting flange to the focal plane is deeper on the Nikon Cameras (one reason why DX lenses can be used on Nikon FX camera, but the same is not true of Canon cameras. Canon's EF-S (lenses like the Nikon DX lenses) will damage the mirrors on Canon Full Frame cameras