Getting a fixed aperture on Nikon lenses?

When using my sisters Nikon with a Nikon 55-200 lens, everything's fine, but when I want to use that lens on my canon (for filming), then the aperture closes up and everything becomes dark. Is there a way I can leave the aperture as is when switching cameras?

The Nikon 55-200mm is a G lens, which has not mechanical aperture ring. The aperture setting is communicated electronically from the Nikon body. But the adapter between the Canon body and Nikon lens has no electronic connection.
You can get an adapter that has a mechanical control over the aperture.
http://www.bhphotovideo.com/...r_for.html
It costs more than your cheapo adapter. The money might be better saved towards a Canon EF-S 55-250mm STM IS.

You don't actually expect Nikon lens to work on a Canon camera do you? Learn a few things about camera systems.

Nope, the default aperture is at its smallest, hence your dark pix. You would need to find some way to adjust the aperture from your Canon camera.