The actual mechanics happen almost entirely between the two lawyers before that date, not at a table both parties sit at together. Your lawyer confirms your mortgage discharge, prepares the statement of adjustments for property tax and utilities, and forwards the signed transfer to Information Services Corporation for registration, while the buyer's lawyer confirms financing has been advanced and title is clear.
For the seller, possession day itself is mostly logistics: keys, garage remotes and access are handed over at the time written into the contract, and your proceeds land in your lawyer's trust account and then in your bank account, usually within a day or two of registration. Any last-minute repair or condition dispute should already be resolved well before this date, because possession day is not built to absorb surprises.
Most sellers find the whole stretch from an accepted offer to possession runs 2 to 4 weeks, occasionally longer if financing or a chain of purchases is involved. Get your hand-reviewed valuation from Joel Dyck.