It's easy to get freaked out over differences that are almost always too small for even an expert eye to notice.
Your technique and creative vision will be 100 times more important in your results with these cameras than any real difference between the D7100 and 70D.
Both are fine cameras. Actually handling both cameras is a very good idea because some people find that Canon and Nikon have a different gestalt and fit and feel different in the hand and in operation.
I have always felt more comfortable with Canon than Nikon. Some fancy that the Canon is more feminine and the Nikon more masculine in a very nebulous way and that distinction sits well in my imagination. Nikon always feel more no-nonsense and macho in its operation.
Having said that however, I just sold all my Canon equipment and have replaced it with Sony, which I don't really know how to describe. Perhaps "intellectual" or "clever" but a bit "cold" and "unemotional".
If this all sounds like nonsense, well it is, so feel free to ignore it - unless that is, you handle the cameras and feel it too. People do bond with their tools/gadgets and if you get that special bond with the design of a particular brand then it helps to make the process of taking photographs more rewarding and comfortable.
The truth is that at the moment - if you are going to spend $1,000 - you are going to get some extremely capable equipment, far better than was available to many of the world's great photographers. And you, with your incredible equipment, are not going to make images like they did. At least not at first, and probably never. But don't let that stop you - I haven't let it stop me.