Two summers ago, left from Quebec city, down to Ogunquit, then north east along the coast of Maine/NB up to PEI. With our 2 daughters. Rules are (always) that we sleep under a roof when there is rain. I'd say 10/50 days.
We *may* ride towards Gaspé/Forillon this summer, although our eldest has reached the friends-first/parents-and-sister-last phase, so not clear. I also heard unpleasant stories wrt locals not wanting visitors (IIRC, access to the Magdalen Islands requires paperwork if you go through PEI/NS -- not clear what they'll to to cyclists
I "think" that Quebec is open to Canadian cyclists (road blocks between Gatineau and Ottawa have been removed), but you'll probably want to double check. Same wrt accommodations. I "believe" that provincial parks have re-opened, not sure at all wrt campgrounds.
I'll follow this thread with considerable interest.