They will be operated by ACR, not mainline. Just a small point as well, technically there is no more CDN Regional, Air Nova, Air Ontario etc. It is all ACR.
I can't remember which routes the 146's will be flying, but YQR-YVR , YXE-YVR come to mind as well as some transborder work (Note YEG-DEN will not return as United Express is starting that one up). As for the CRJ's in Ontario, I don't have a clue which cities they will serve.