Here's a rough itinerary - emphasis is on planning up to the ferry ride back to the mainland, because those have to be booked in advance. Everything else is flexible.
Day 1: Toronto to Quebec City KOA (781 kms)
Day 2: to Baie Comeau (camp at Manic 2) (436 kms)
Day 3: to Lab City (582 kms)
Day 4: to Happy Valley Goose Bay (530 kms)
Day 5: to Port Hope Simpson (405 kms)
Day 6: to L'Anse aux Meadows (ferry to NL) (355 kms)
Day 7: to Gros Morne National Park (314 kms)
Day 8-10: camping/hiking - no riding
Day 11: to Corner Brook (172 kms)
Day 12: to Cabot Shores, NS (Cabot Trail) (ferry to mainland 5-7 hrs, departs in am) (309 kms)
Day 13: camping/hiking, no riding
Day 14: to Meat Cove (camping at top of Cabot Trail) (88 kms)
Day 15: to Inverness Beach Village Campground (other side of Cabot Trail) (130 kms)
Day 16: to somewhere on the east side of PEI
Day 17: to somewhere on the west side of PEI
Day 18: Gaspe Peninsula day 1
Day 19: Gaspe Peninsula day 2
Day 20: Gaspe Peninsula day 3
Day 21: to Quebec City KOA
Day 22: to home.
Give me a shout when you get to the PEI part of this route! I'll send you a PM