These places I have visited, all began driving from Toronto: Newfoundland, Nova Scotia , Cape Breton I, PEI, and the Gaspe penninsula.
Newfoundland is by far the best. PEI was pretty boring. Heard great things about the Cabot Trail on Cape Breton Is. but I was underwhelmed. Gaspe (town) was nice, but a long way to drive just for that. After a week of driving around Nova Scotia, my teenaged daughter announced form the back seat of the rental car: I'm not getting out to look at another lighthouse!