An executor's authority to act, sign a listing agreement, accept an offer, comes from the will itself once probate is applied for, but a buyer's lawyer will still want to see the grant before releasing funds at closing. That is a title requirement, not a preference either side can waive.
The practical fix is timing. File the probate application with the Court of King's Bench as early as possible, and structure the purchase contract's possession date with enough lead time that the grant is expected to arrive before closing rather than after it.
While the estate works through this timeline, get the property priced correctly rather than guessing. Joel Dyck's hand-reviewed valuation accounts for renovations a previous owner made without a permit, which public records and an online estimate cannot see.
Get your hand-reviewed valuation from Joel Dyck.