I rode the Waterfront Trail from Niagara Falls Ontario to Kingston Ontario. My comments from a year and a half ago are at this link:
Bike Tour near Lake Ontario and part of Erie Canal - June 2024

If you have a chance to get provincial highway maps when you cross into a new province, grab one. And sometimes you can get good information on the provincial parks that have campgrounds. Some of the parks in Nova Scotia had hike-in campsites that were more secluded and better grass to pitch tents than the sites designed for cars and RVs. I was in Nova Scotia in 2019, got a booklet of the provincial parks there, which helped a little bit for my planning, but the state highway map was much more useful than the provincial parks booklet.

Do you plan to go to Prince Edward Island (PEI), or bypass it? If you go to it, you have to cross a bridge. They do not allow bikes on the bridge but when I was there in 2019 there was a shuttle available to take me and my bike across the bridge. At the south end of PEI there is a ferry to Nova Scotia. At that time, you paid nothing to cross to PEI, but paid a fee to return to the mainland.

I did not buy a sim card for any of my Canada trips, so I can't make any suggestions on that.