We landed at the Rainbow Bridge - no problems. All three Buffalo/Niagara crossings do landings. I think I wouldn't mess with Quebec. Pretty sure they don't have Immigration at Billy Bishop.
If you applied to sponsor while living abroad, you need to be with him when he lands. One of the conditions of his approval was your promise to resettle in Canada, so be there for his landing.
As has already been said - he will need to provide an address in Canada that they can send his PR card to. He is okay to go back after completing his landing - to tie up loose ends and prepare for the move. I don't know whether - being visa-exempt - he has to get a travel document. He will still have a copy of his COPR and the PR visa affixed to his passport after his landing. That should be sufficient but, since I didn't leave Canada before getting my PR card, I can't confirm for certain. Hopefully someone will log in and answer that question through their own experience.
One thing: be sure he lists his "Goods to Follow" on a
Customs Inventory Sheet to take with him when he lands. He'll need to submit that to Customs after his landing is finalized so that he'll be able to import his belongings when you later complete your move. Otherwise, he'll end up paying duty on everything that you guys bring into Canada later.