For puffins, you need to go to Newfoundland, (pronounced newFUNland) if you go to PEI go to the New Glasgow lobster supper. Order the 1.5 lbs lobster and fill you face. There are a lot of online stuff about different lobster suppers but my wife grew up on the island, I have been going there may whole life and when my daughter wanted to get married on PEI, we modeled the reception after the New Glasgow lobster supper. If you want to know what an East Coast family lobster boil is like, New Glasgow is the one. Trust me.
Can't comment on music festivals other than to say the East Coast Music Awards are usually a good time. For Whales, do research for whale watching in the Bay of Fundy, depending on your time of year it may be Digby or St Andrew's in NB (Which is a hidden jem)
Let me know when you are thinking about going, maybe I will be out East or able to hook you up. (It is rhe East coast way)