More likely 2027 if they keep the very optimistic schedule! The schedule in that June 2018 report was based on a Q3 2018 start on tendering for 100 more vehicles. Then an RFP in Q3 2020, award in Q4 2020, prototype delivered in Q2 2020, and final delivery didn't start until Q2 2024 - continuing for 2 years of deliveries. Which seems highly optimistic!That's easy to answer. Bus service on 1 or more routes with tracks between ~2020 through 2024 (if they order immediately from someone else; otherwise 2024 gets later).
For comparison, the current project started back in April 2006, An RFP in 2007, with the award to Bombardier in 2009, first prototype in September 2012, deliveries starting in May 2014, and with the 100th car arriving in September 2018.
If the new streetcars follow similarly, then car 100 wouldn't arrive until 2031!
Meanwhile TTC estimates they'll need over 64 streetcars by 2023, and over 304 cars in 2027.
Which means if they go for just 100 more in a new tender, instead of first getting the 60 from Bombardier asap, and then 100 more ... then they'll be running buses every year in the future!