Hi Christian,
I haven't used it, but the Nikkor 105mm is a legendary lens. It's been popular since it was introduced originally for Nikon rangefinder cameras in the 1950s, was redesigned for use on SLR models in the late 50s and has been produced in many versions since, even including macro (Nikon calls it "Micro") and PC (perspective control) versions. There is currently a 105mm Micro-Nikkor VC (vibration control) in the modern lens lineup.The one you have sounds to be "just" a short telephoto... not macro or PC. That's fine, though. You should find it useful.
A Nikkor-P is what's called a pre-AI version of the lens, earlier type that won't work fully with later Nikon cameras... But I think will be possible to adapt to Canon just fine.
However, I don't care for either of the adapters you pointed to. In fact, the second one is a Canon FD to Canon EOS/EF adapter and won't work at all. The first one is a simple Nikon to Canon EOS/EF adapter without a chip.
And the prices for the adapters seem high on Amazon.
Here is what I think is a better adapter on eBay
. The key is that this has an electronic chip that will allow focus confirmation to work on your camera. This is important, because it can be difficult to focus lenses manually with modern DSLRs, because their viewfinders are smaller and dimmer (even though the 7D's viewfinder is better than many of them). Some of these "chipped" adapters also let you program the lens focal length and aperture into them, if you wish, so that the EXIF in your images records that info correctly.
I don't know that particular adapter or seller on eBay. There are many sources for these adapters, some in China and Hong Kong, many of which seem fine, too. But I bought a similar adapter from China recently, except it was for a Tamron Adaptall2 lens. It was delivered rapidly and safely and works fine.
Personally I haven't adapted any of my old Nikkors yet. Some day I might, but I just don't urgently need any of the focal lengths. All my Nikkors are AI or AI-S manual focus and I am certain they can be adapted. I am a little uncertain if you will have any trouble adapting a pre-AI lens... I don't think so, but hopefully someone who is more familiar with those types of lenses will jump in here and clarify.
You mention "lens cap" labelled "105/2.5, 135/3.5".... I think you mean lens hood, not cap. If so, the hood is probably usable on more than one lens and that's why it's labelled that way.
It's not as easy to shoot with a strictly manual adapted lens, as it is a modern AF lens. Manual focusing isn't all that big a deal, especially when you have AF Confirmation available (thanks to the chipped adapter). The aperture control will also be manual and I think is a bigger deal. You'll need to learn to do "match needle metering" with your camera (check the manual). And you might want to manually open the aperture during focusing, so that the viewfinder is as bright as possible... Then stop down to the aperture you have chosen to use. It's more difficult to focus with the lens stopped down significantly, because the viewfinder gets dim.
This macro image was made with the adapted Tamron lens I mentioned above...
It's trickier using a fully manual lens with a moving subject like a bee... But is possible as you can see. Stopped down to f11 the viewfinder is quite dim and AF confirmation no longer works.
