Buses will not handle the expected demand. Even if there exists an option to accommodate the required volume of buses at the Port Lands / Commissioners end, those buses would swarm the street space at the downtown end of the route.
On the other hand, tabling a short, dedicated subway line as a Plan B, might be a good idea. Something similar to Montreal's yellow line, that only has 3 stops, and connects the Berry-Uqam interchange with the island and the south side of the river.
A subway would cost more than LRT, but:
1. That would be a short route, 4-5 km, thus comparable in price to a 10-15 km long LRT project. Not something unaffordable.
2. Some posters here expressed concerns that LRT might not actully have enough capacity if/when the area is fully built up.
3. Even though the new subway would be very short initially, such a project would include a new tunnel and one or two new subway stations in the downtown. That means, the other end can be extended much further north, and turn into another Relief Line if/when the need arises.
No need to scrap the LRT project. Just table both the LRT and the subway option, and let the provincial government pick one.
If they are again any LRT (especially given the current Finch LRT troubles), and would rather fund the subway - that works. If they would rather save money and fund the LRT - that works too.