What if Charles XII was able to get the Ottomans to join the war, and open a Ottoman front?
When? If it's after Poltava there's really not much they can do because Peter invaded the Ottomans anyway because they were harboring Charles XII and a few of his soldiers in Tighina/Bender.
When? During Charles's great victories at Narva and Klissow, and Fraustadt? It would definitely keep the Russians occupied but I'm not sure Sweden could hold the tide. At best they could get some token concessions that firm their hold on the Baltic but nothing really major, at least against Russia. They could probably really deal a smackdown on Denmark, but you have to consider how the rest of Europe would react to a rising Sweden.And if it was before Poltava?
What if Charles XII was able to get the Ottomans to join the war, and open a Ottoman front?
He did. The Ottomans went in halfheartly and managed to surround the Russian army and Peter then gave away Azrov and there was peace again