From the list of options on the table, central BRT lanes are probably the best. Indeed, they can be converted to LRT in future. This is easier than upgrading from curbside BRT to central-lane LRT.
Hydro corridor is too far from many trip generators along Finch West, particularly highrises and the hospital on the south side of Finch between Dufferin and Bathurst. Plus, to extend the BRT along that hydro corridor, one has to deal with a number of obstacles such as Ross Reservoir (east of Dufferin), soccer fields near Bathurst, and the TTC parking lot near Yonge.
At the same time, the travel time reduction due to the use of hydro corridor vs Finch would likely be minor. The corridor does not run all the way into Etobicoke along Finch, it veers south just west of Hwy 400. Moreover, there are obstacles west of Jane, and Finch / Jane is a major trip generator, therefore the BRT would likely use the hydro corridor between Jane and Yonge (8 km) and then switch to Finch proper anyway. The travel time difference for those 8 km: Finch - 21 min at 23 kph, hydro corridor - 16 min at 30 kph, plus 1 or 2 min to make turns to/from Jane. Real time saving: 3-4 min at best.
Other proposals that make sense are artic buses, and POP / all-door loading.