Do you currently have a DSLR? If so you should stick with that brand as long as the lenses will be optimal for the new camera.
If this is going to be your first full frame system it is hard to say without knowing what is more important for you. The a7r2 is about 1000 dollars less then the third gen that just came out, but in my opinion and watching reviews, the a7r3 is worth the extra money for the extra and improved features such as 2 sdcard slots, a better autofocus system, bigger battery, the evf is a lot better, etc. So from spec wise comparison the a7r2 and a7r3 are worth their respective price
Keep in mind with these types of cameras you do need to think about the lenses. There are mixed things with using adaptive lenses (ie using a canon lens with lets say a metabones adapter) but that can equalize the playing field a little bit, but using native lenses is better. The issue with Sony lenses is that they are a bit more expensive then the Canon counter part and Sony does not have as many lenses as canon or nikon. Regarding the adaptive lenses, there are some issues with them like the auto focus not working as well as native, but on my a7r2 I have a sigma 24-105 f4 with the sigma mc-11 adapter which works really well for my needs.
The only linux related thing I can add right now is that if you are going to do raw processing on either camera, make sure darktable is the most up to date and keep in mind that at full res the size of the raw files are almost 90mb each, so a fairly powerful computer might be needed.
So to answer your question directly, I do think the a7r2 is worth the money, but the a7r3 is worth the 1000 dollars if that is within your budget.