我认为两个词是没有区别的，事实上我字典里interplay的解释是“To act or react on each other; interact ” 也就是说两个词本身就是
同义词。如果硬要说用法上有什么区别，我认为那就是interplay本身作名词的时候意思仍旧保持不变，而interact的名词是interaction。
例句：
Interplay(本身就有名词用法，如下面例句)
•We can examine the interplay between the different questions, to find out how people's judgements are formed.
•These results are determined by the complex interplay of several feedback processes involving agents, resources and memes.
Interact （动词，搭配with）
•Interact with an audience is being evaluated
Interactive
•But we would run an event for you on how to create interactive learning activities in Word.
•Once you become interactive you will know you are never alone.