1) Do you any difference between Aristotle's definition of Tragedy and Dryden's definition of Play?

Yes, there is difference between Aristotle's definition of the tragedy and Drayden's definition of play.

Aristotle's definition of Tragedy, 

' TRAGEDY IS AN IMITATION OF AN ACTION THAT IS SERIOUS, COMPLETE AND OF A CERTAIN MAGNITUDE IN THE LANGUAGE EMBELLISHED WITH EACH KIND OF ARTISTIC ARGUMENT THE SEVERAL KINDS BEING FOUND IN SEPERATE PART OF THE PLAY'

Dryden's definition of play : 

"A JUST AND LIVELY IMAGE OF HUMAN NATURE REPRESENTING ITS PASSIONS AND HUMOURS AND THE CHANGE OF FORTUNE TO WHICH IT IS SUBJECT, FOR THE DELIGHT AND INSTRUCTION OF MANKIND"

We understand it in three parts :

1)  a just and lively image of human 

2) representing its passion and humours and the changes of fortune to which it is subject.

3) for the delight and instruction of mankind.

Both definitions are very nearly same and some are different points but also languages has been changed and talked about the imitation with human being as well as languages. After the Aristotle's definition of the tragedy, Dryden was the first who tried to give a well formed definition of the play. There are some points we can see that difference in both the definition. In the definition of tragedy Aristotle talks about imitation of action. While in the definition of play Dryden talks about a just and lively image of human nature. We find something is that, they both talk about the imagination but in different way. Aristotle talks end with the definition with pleasure and catharsis.

 2) If you are supposed to give your personal predilection, would you be on the side of the Ancient or the Modern? Please give reasons.

I like to be on Modern side. There is many reasons for this, 

First of all there is newness in this and many new concept of writing and science and technology ,new knowledge , new manners , new ideas and information etc..

But it is also true that this all are found in our root which is ancient without ancient there not be Modern thought or ideas. Generally We can find that mostly modern takes idea and anything from Ancient but it tries to present different way and by the unique manner. Many times mix up modern and traditional thought then became a new manners. But in modern there are many ideas and new form of writing.

3) Do you think that the arguments presented in favour of the French plays and against English plays are appropriate? (Say for example, Death should not be performed as it is neither 'just' not 'liely' image, displaying duel fight with blunted swords, thousands of soldiers marching represented as five on stage, mingling of mirth and serious, multiple plots etc.)

I am not in favour of french drama or in English drama because both are correct in their own place. French drama followed the three unity for make their plot strong and otherside English drama has plot and subplot which we don't find in french drama but subplot makes drama interesting people stay attached with it and enjoyed it. French play only focus on unity while English drama focus on many things together. And that's why I found English drama more interesting.

For example I saw one play on hard times  which is based on novel. In which main plot was about marriage and class difference but subplot is industrialization,

Which audience enjoyed and stay connected with whatever going on.