I was there in 2019, so pre-covid.
I was camping. I did not have a sim card for my phone, so had no data. I got on the ferry for PEI which had wifi so I could get a weather forecast and saw that there was five consecutive days of rain forecast, and I remembered that there was a hostel in Charlottetown. I completely rewrote my plans while on the ferry and made reservations to stay at the hostel on Canada Day weekend. That was the best way to spend the middle part of those rainy days, indoors instead of in a wet campsite.
I rode their rail trail some, the Confederation Trail, it was well maintained. And I enjoyed the sightseeing in Charlottetown the best I could, in the rain.
The ferry was free to cross onto the island, they charge to leave. (Reminds me of the song Hotel California.) The ferry is approaching the port in the photo below.
My bike on the ferry.
Probably half of my distance on the island was on their trail system, half on roads.
Their trail system.
This was the second rainy day as I was approaching Charlottetown where I would sleep indoors for three nights.
They do not allow bicycles to ride across the bridge, must take shuttle. When I called them on the phone to say I needed a shuttle, they said it would take a few extra minutes as they needed to hook up the trailer for my bike. I had four panniers and a rack top bag, I was afraid they were going to charge for all the additional luggage after the first bag, but they only charged me the fee for having a bicycle. These are 2019 prices, likely have gone up since then.
They did a good job of securing my bike to the trailer.
And the ride across the bridge to leave.
I am not a Canadian, thus I was ignorant of much of the history of the role of the Confederation Papers that were signed in Charlottetown and the origins of Canada Day. I wish I knew more of the history before I went so I could have enjoyed the historical sites more.
If you have never seen Bay of Fundy, if you were camping I would suggest one of the hike in campsites at Five Islands Provincial Park in Nova Scotia, but you said you probably are not camping.
I spent five weeks in the Maritimes, I can't really think of anything unique to PEI, that is why I have little to say on what to see. And most of my time there was raining, so I do not remember seeing a lot either.
If you change your mind and camp, bring repellant for the bugs.