I made home made chicken fingers a couple nights back. I simply deboned breast half, and a thigh. I sliced the chicken into strips. I lightly salted it, dipped it in egg wash, then into a zipper bag with seasoned flour. I let it hang out in the bag for about five minutes, giving the flour a chance to glue itself to the meat. After that, the meat was removed, a piece at a time, bounced against my fingers to remove excess flour, and placed into 360' oil for deep frying. By the time the coating was lightly browned, the chicken was cooked through, but not overcooked at all. It was so tender and juicy that you would swear you'd had an expert in the kitchen. But it was just me.
I still maintain that you don't need to do much with chicken to get it tender and succulent, other than cook it to the correct temperature. This has been true for me with fried chicken, chicken fingers, barbecued chicken, grilled chicken, roasted whole chicken, tempura chicken, panko coated chicken, etc. Oh, and choose a fryer. It's a young chicken that hasn't yet had a chance to toughen up. Roasters tend to be older hens that are made for stewing, long roasting, and soups. They are larger, and can be tough if cooked quickly.
Marinades are acidic. Acids cause muscle fibers to tighten up, resulting in a tougher outer surface. The marinade doesn't flavor the inner meat, just its surface. A brine contains no acidic ingredients, and will flavor the meat all the way through. A proper brine can also tenderize meat.
There are enzymes in milk and dairy products that will help break down muscle tissue, rendering the proteins more tender. I use milk sometimes to help tenderize lean pork, or chicken. Raw pineapple (not cooked or canned) will also tenderize meat, as will papaya, and kiwi.
The things I post are proven methods, that I have learned from others, or by experimentation, and are used in my kitchen every day. When I don't know something, I ask, try the answers I get, and use the techniques that work. Then, when I'm satisfied that I can duplicate the results every time, I share them with anyone and everyone.
Hope this helps.
Seeeeeeeya; Chief Longwind of the North