I loved Cape Breton, and not just the Cabot Trail. I was somewhat disappointed with mainland Nova Scotia. For the coast between Yarmouth & Halifax, you've got to get off the main road to have the nicest scenery and to avoid heavy traffic. That will more than double the distance you cover. I couldn't get excited about the Annapolis valley or the interior.
I thought that PEI was OK but not great. We arrived there by ferry from the Madeleine Islands, which although part of Quebec, is closer to Cape Breton & PEI than mainland Quebec. Anyway, we loved the Madeleine Islands, though biking there is challenging due to everpresent strong winds. PEI seemed dull by comparison.