1) You book int'l -> YYZ/YVR/YUL/YYC -> domestic destination
2) Regardless of what you book, you have to partake in the moronic "mandatory hotel quarantine program" at the point of entry
3) In most cases AC will automatically rebook your domestic connection flight for three days later, otherwise you can do so by calling AC
4) If your negative test result comes back early, you can continue your journey after 1/2 days vs. staying the full three nights
5) If you choose to fly home earlier, you can again contact AC to be rebooked on an earlier flight which they will do free of charge as long as there is availability