my two cents between Charlottetown, PE and St. John's, NL.
Charlottetown
Min Su Cafe, on Water Street = Best Bi Bim Bap (korean salad) I've had (admittedly, I've never been to Korea) and the owner is a real gem.
Merchantman Pub, also on Water Street = Pub food with the occasional gastronomic twist, highly recommend the Tupelo Street Chicken, if still on menu.
Downtown Deli, on Grafton = Best sandwiches in town (sorry, Leonards, you beautiful German delicatessen, but the Lebanese have you beat).
St. John's
Get Stuffed, on Duckworth = Great name, great food, great prices and $1 hot dogs on the menu for your picky partner.
Sun Sushi, on Duckworth and Stavenger = The Stavenger one seems better for the entire menu, but is an ugly location. You can't go wrong with either for sushi. (disclaimer, i only eat veggie rolls, so perhaps not a real endorsement for real sushi, but if you like spicy broccoli roll...)
Crane's, located in a North Atlantic, down the Southern Shore = admittedly not a restaurant, more of a truck stop, but they have a solid chips, dressing and gravy, and their custard cone machine is only broken 8 months of the year.
Charlottetown has a more ethnically diverse population, and therefore better food in a wider variety. No offence to St. John's, but you could stand to lay off the salt a little.
-foundnewland