I rode from Ottawa to NB via NS and PEI about 15 years ago. I crossed into Que at Hawkesbury and rode
#158 to Berthierville to bypass Montreal. In retrospect, I wish I had gone through Montreal and hung out a bit. From Berthierville, I followed the St. Lawrence north shore through Trois-Rivieres to Quebec City (both cities were very hospitable to a touring cyclist), crossed on the Levis ferry and rode the
#132 on the south shore to Riviere-du-Loup. There I picked up the Petite Tamis, a stone dust (old railway line) trail which runs about 134km to Edmundston. You can find camping and other accommodations, and food just off the trail, and every road crossing has little signs that indicate where services are and how far you have to go. I camped at a park (think it had something to do with Yogi Bear) which was about 100 meters off the trail, about half way to Edmundston. The trail is mostly downhill from RdL, but it's dusty and my bike was pretty filthy when I got to Edmundston. There's a NB provincial campground just inside the NB-Que border and it had cycle-only camp sites. I was only cyclist and I had a grassy place to put my tent, bike racks built into the ground, and my own comfort station! Nice. And there was a pub/restaurant in the adjacent town about 10 minutes away.
I continued down through Fredericton and then Saint Johns where I crossed on the ferry to NS. I followed the Annapolis Valley to Windsor and then turned left and headed cross county towards Truro and finally up to Pictou where I caught the ferry for PEI. I spent a week exploring the island, based in Charlottetown at the Southport RV park. There's no tenting there, unless you're either a hiker or cyclist. There's a Tim Hortons just across the bridge and plenty of pubs and restaurants downtown, about a 5-7 minute ride from my campsite. It made the perfect place to take day trips to the north shore unloaded. After 4 nights I moved on to the west end of PEI.
Where I to do this again, though, I think I'd stay on the St. Lawrence south shore a bit further and then route myself over to Campellton and Bathurst and follow the coast down through Acadia to Shediac and then take the shuttle over the bridge.