Those are probably the nikon to canon ones. Which is the canon EOS to F mount adapter u saw ? Care to share ?
Canon EOS systems have a shorter lens flange to focal plane distance compared to Nikon. To have such an adapter it will not permit the canon lens to focus to infinity, or it will contain corrective glass of some kind and end up like some teleconverter, and not to mention the need to incorporate some kind of mechanism to allow the aperture control. I have heard of one such exotic adapter with corrective glass on overseas forum thread , but i never actually seen one even on ebay before. ( Makes one wonder if it actually existed ). You will probably lose some IQ, or a fraction of stop of light, and pretty expensive.
Even the older Canon FD mounts need to be specially machined to fit an F mount.
Even if you find a mechanical adapter and can achieve focus the main question will be: how do you want to set the aperture? EF and EF-S lenses don't have any aperture rings. All EF and EF-S lenses need to get the setting from the camera as electrical signal. The electrical systems between Canon and Nikon are incompatible. Better check which features you are missing on the Canon body and see whether they are achievable by other means.