The Museum-St George and King-Union curves are functional, but TTC hates them and would not build anything similar these days. Such tight curves are not good for wheels and tracks, and are too noisy for riders. That applies to standard size subways, but a mini metro might be able to handle tighter curves.
On your map, there are at least 4 (maybe, even 6) rather tight curves on the Sheppard line.
For a one-seat ride across the north of the city, converting the existing Sheppard subway to some kind of high-floor mini metro might actually be the best bet if that technology is cheaper to extend. If it is extended as subway, it will probably never go east of STC because of the construction costs. In the west end, the probability of going past Downsview depends on the construction costs, too.
I used to be in favor of a subway / LRT combo solution; extending the subway to Agincourt and building LRT east of that point. I personally do not mind transfers, but it appears to be a big issue for many people. If so, maybe we should think how to eliminate that transfer. But if the subway is extended, my concern is that it will never go past STC due to the cost. On the other hand, converting the existing subway to low-floor LRT is costly, and is guaranteed to anger many existing riders. Therefore, I am trying to think outside the box, although not sure if the mini metro option is viable in this case.