For better or for worst, a lot of characters share similarities with or parallel each other because it's circumstantial. How a character relates to others or is expressed through the story changes depending on the current events and/or who is interacting with who. With Kaneki, he in general has always been a "parental" character, so he often parallels other parent characters. Occasionally when Touka or Ayato are around attention is brought to how similar to Arata he is, pre memories returning when he was closest to Arima and compared to him he was the "parent of the Quinx", and now that Eto is taking more center stage there's a bit more to read into Kaneki and his similarities to Yoshimura. What Eto and Kaneki have in common is a severe feeling of neglect from a parent figure, so seek out that attention from others. Kaneki gravitates towards domineering woman, and while admittedly Eto is a little harder to pin down, she gravitated towards someone who is well intentioned but selfish/unsure of how to take care of his loved ones.
TL;DR, Kaneki and Eto see their "mother" and "father" in each other respectively.
Eto is an interesting case though since her "affections" can be interpreted as blurring the lines some.