We've done Ontario break several times now. Like Disney, it helps to be early and get the headliners done first. By afternoon lines start getting long, and the FOTL passes are a big expense that I don't want to pay.
Note that this applies to the park in general; the WWOHP in US area will be swamped and will probably lower lines in some other areas of the park. WWOHP in IOA has calmed over the years, but with the P2P between the two on the Hogwart's express it might see a resurgence.
We are looking forward to US this year as WWHOP has openened, as has Transformers since our last visit, and Despicable Me was way too long a wait for us try. Last time there, there was hoarding all over the place. I think it will almost be like a new park with all the changes.
ETA: And no, the parks don't feel quiet as busy as Disney from a crowd level aspect, but the rides don't generally load as quickly, so lines often seem longer (IMO).