I don't think Ellis is on the market. He is just a popular trade candidate on this site by Maple Leafs fans for the most part. I don't see him actually being traded other than for fun on this site.
eh he doesn't really push the needle and has an expensive QO for what he brings
So the short answer to your question will be that there isn't many. They will likely either need their game moulding by a coach to fit the system, or they will be expensive. Likely both. Theres a reason New Jersey were able to get Hall for Larsson.
I truthfully dont think there is a viable "top pairing" option for Toronto that either they would want or the other team would want to trade to Toronto for the pieces theyd be offering. At least for this year/offseason.