The character who discusses the relative merits of French drama and English drama in Essay of Dramatic Poesy is:

The correct option is Lisideius.

John Dryden's famous work of literary criticism, An Essay of Dramatic Poesy (1668), is structured as a dialogue among four speakers who debate the principles and merits of different dramatic traditions. Each character represents a specific critical perspective:
• Crites argues in favor of the Ancients, praising classical Greek and Roman drama.
• Eugenius argues in favor of the Moderns, asserting that modern writers have improved upon classical models.
• Lisideius champions French drama, arguing that French plays are superior to English plays because they strictly adhere to the classical Unities (Time, Place, and Action), maintain decorum, and avoid the mixing of tragedy and comedy.
• Neander (representing Dryden himself) defends English drama, arguing that while French plays are more regular and neat, English plays have more vitality, variety, and emotional depth.

Therefore, Lisideius is the character who introduces and discusses the merits of French drama relative to English drama.