The words canape, canopy sound the same but have different meanings and spellings. Why do canape, canopy sound the same even though they are completely different words?
The answer is simple: canape, canopy are homophones of the English language.
Alternative spelling of canapé.
A covering, usually of cloth, suspended over a throne or bed or held aloft on poles above an eminent person or a sacred object.
Architecture An ornamental rooflike projection over a niche, altar, or tomb.
A protective rooflike covering, often of canvas, mounted on a frame over a walkway or door.
A high overarching covering, such as the sky: "I just look up at the stars and let the vastness of that black and twinkling canopy fill my soul” ( Margaret Mason).
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").