The closest farmer's market to you will be located in Summerside. It is open every Saturday from 9 am to 1 pm. Charlottetown is not that much farther and has a few markets to choose from. From early July to the end of August, the Downtown Farmer's Market happens every Saturday. The Charlottetown Farmer's Market operates every Saturday year round and on Wednesdays during the summer months. The Riverview Country Market offers fresh produce and meats Monday through Saturday and seasonally on Sundays.
I don't know if I could really choose one as the best - they are all pretty fantastic!
You will also small roadside stands, u-picks and local butcher shops for fresh meat all around the Island.
Enjoy your visit!