I'd want a bridge over to the airport. Here's my logic, and I accept that many will probably disagree with it.
Build a bridge over to the airport at the foot of Bathurst. This would naturally have streetcar tracks built into it, to branch off the Queen's Quay streetcar. But I think that once real HSR talks start building between Ontario and Quebec (not actually that long, it would seem,) Porter's days will be numbered. With a link from Toronto to Montreal, Porter will see a huge loss in revenue, since HSR trains would be about as fast, but would go from city centre to city centre, and will be around the same cost. The airline will have a hard time operating out of City Centre airport with trips to Sudbury and Thunder Bay as the biggest intended draw. Once this comes along, the airport will once again be without a server, and so could be closed and Toronto Island could be turned permanently into a park-only zone, with the bridge to be rebuilt into a pedestrian and transit-only access. This would allow a streetcar/LRT to run through the island year round, perhaps connecting through a similar bridge along the eastern gap. With year-round access, the island could become a much more significant tourist attraction, and connections from the West and East would make it almost like the Central park of Toronto.
Or at least that's my idea. It'd mean an end to the ferries, would increase mobility to the island, and would result in a huge amount of new parkland. Then again, in that dream, there's also a parliament subway going down to Cherry street and underwater to the end of the Leslie spit, which is populated by tropics-themed condos and hotels/resorts. But I think the idea that Porter would go down considerably after a significant HSR is built is sound logic, and also that we shouldn't be building a tunnel that would serve a single purpose that could be basically obsolete in less than 30 years. Also, a streetcar/LRT link would be good to further encourage mass transit to the airport.