Can the limitation period run differently against different defendants in the same claim in Ontario?

Yes — because Ontario's discoverability rule under the Limitations Act, 2002 asks when a claimant knew, or reasonably should have known, that a particular person was responsible, the limitation clock can genuinely start at different times against different defendants in the same overall dispute. A claimant might know right away that something went wrong and who was directly involved, while only learning of a second party's involvement, or that they were even a potential defendant at all, considerably later, perhaps through discovery in the existing case or new information that surfaces afterward.

This matters practically when a claimant wants to add a new defendant to an existing lawsuit after the two-year period from the original incident has passed. If the claimant can show they genuinely didn't know, and couldn't reasonably have known, about that particular defendant's role until later, the clock for that specific defendant may not have expired even though it has for others already named. Because this depends heavily on what the claimant actually knew and when, and what a reasonable person in their position should have investigated, documenting exactly when new information about each potential defendant came to light is important if a later addition to the claim becomes necessary.