Odds are very high that this Ontario Line proposal won't get federal funding, and thus not be built.
1. As was mentioned earlier this week, the Provincial government has already positioned themselves to blame Trudeau if the Ontario Line doesn't get built. I believe it was last month where they scheduled a whole press conference to blame the Feds for not providing funding to the line. And keep in mind that the Business Cases Analysis still hadn't been released at that point, so it was literally impossible for the Federal government to contribute funding. That's a very odd move, if you genuinely wanted the funding to come. Honestly I wouldn't be surprised if this Business Case has some fatal flaws built in, specifically so the proposal cannot receive federal funding.
2. As per my previous post, assuming the government does intend to use smaller trains, capacity will be inadequate on the Ontario Line. It's very easy for the government to justifiably deny fundings on those grounds.
3. This mysterious "new" technology. The fact that the government seems to be proposing some kind of new technology should raise red flags for everyone. Rail is an extremely mature technology, and Toronto and the TTC are far from being the busiest and most crowded cities and metro systems in the world. If the Beijings, Londons and Tokyos of the world haven't found some magical new technology for their systems, its highly unlikely we'll develop anything worthwhile here. I'm expecting this "new" technology to end up being good-old LIM, but if it's indeed something new, it probably isn't getting federal funding, and rightfully so.
4. Most importantly, Ford is extremely unpopular in Ontario, and even more so in Toronto; far more unpopular than Trudeau. It's very easy for Trudeau to say that the plan is garbage, and that the Provincial govenremt is uncooperative, and I'm sure people would eat it up.
If the federal government doesn't provide funding, presumably in the hopes of a friendlier government in three years, it won't be a huge setback, as the Relief Line South was pretty damn close to shovel-ready, while the Ontario Line is essentially starting from zero. We'd likely lose a year at most, relative to a realistic Ontario Line timetable. From a network building perspective, this is likely a favourable outcome, as the Relief Line South + North is a more robust plan, and costs around the same amount of money anyways.
I'll wait for the BCA to make final judgement, but unless concerns over Ontario Line capacity are alleviated, I'll be hoping for the federal government to deny funding to the proposal, in exchange for Relief Line South + North funding three years from now.