The travel agents guide to schedule changes may be helpful: https://www.aircanada.com/content/da...nge_policy.pdf

In general, based on my experience over the past year and a half, where I've had multiple schedule changes, ac will do the following, based on your preference:
1. Refund your flight
2. Rebook you from your origin to your destination as closely as possible to the times you had for your flights
3. Rebook you on whatever itinerary you want, within reason, as long as the origin and destination are the original ones, and there's class availability, and it's within a few days +- from your original date of travel. See the travel agent guide for details on these rebookings.

YMMV - I use Air Canada for Business almost exclusively, but this also happened to me with 2 bookings with OTA (expedia) described below:
For the first, we ended up getting a refund, then we rebooked on AC for the same cost but in PY, and for my inlaws, for $200 less /pax.
For another, we had looked at alternative flights (yfc-yul got cancelled on a yfc-yul-nrt trip, so our yfc to yul was moved to an early morning. We decided to stick with it and spend some more time lounge hopping between MLL and National Bank lounge.

With AC for business, I've never had any issue getting changes done after a schedule change, within those parameters (same origin/destination).
For example:
One time I had YFC-YOW-YYZ-ZRH-ARN that I booked to avoid turboprops (and enjoy *A/PP lounges at ZRH, which are excellent.)
It was changed completly due to scheduling changes dropping connections below MCTs.
Called in and got rebooked the day before, same route, 0 issue.
Had changes bump me into O, and let me use eUps early on too, which is nice. Happened on a recent flight to TLV. And I ended up taking a few more days due to the change.

Good luck - and keep in mind the phone lines are swamped due to res system change.