^I've mentioned it in other threads but I love Tokyo's central ring transit system architecture (the system architecture not the building architecture). Toronto is not a Tokyo sized city but other small cities like Vienna also achieve a kind of ring-system on a smaller scale.
Toronto might not be as big as Tokyo, but among developed world cities that are as big as Toronto will be in a few decades (10-12m people), they pretty much all spread out their office supply and transit access beyond a single a point, whereas Toronto is still pretty downtown/Union Station focused.
They don't spread out too much though, most of the office space and transit hubs are still within about 10km of the city center. That means the equivalents for Toronto would be mostly within Old Toronto (East Harbour/Portlands, Liberty Village, Yonge-Bloor, Bloor-Dundas/Junction Triangle, Yonge-Eglinton, Danforth Village).
The further from Downtown you get though, the longer the distances involved in connecting nodes to each other and to their adjacent neighbourhoods with rapid transit, and also, these more distant nodes have more arterial roads and highways serving them that will remain relatively competitive against transit, even with congestion. Toronto might still be able to get some relatively strong nodes approx 15 km from downtown, due to the relatively high suburban densities that will exert somewhat of a "gravitational pull" towards these more outlying nodes and make them more viable as traditional CBD styled places, but we're still talking about places like NYCC, ECC, Kennedy GO/Golden Mile. I think if tax rates are adjusted to be more competitive with the 905 suburbs, and transit access is expanded, these could do well in attracting new office space.
But I think the Pickering, Mississauga, Vaughan, Markham, Oakville, Newmarket, etc growth centers will be at a disadvantage compared to NYCC/ECC in terms of being more far flung and located in more auto-oriented contexts. They might have the potential to eventually become like NYCC is today, but NYCC also has the potential to be more like Midtown or even Bloor-Yonge in terms of urbanity imo. So I think it's good to try to create more urban nodes in the outer suburbs, but the potential of the nodes 2-15km from downtown shouldn't be overlooked either.
The large pool of workers available to downtown employers is also a major advantage, with higher densities of the neighbourhoods South of Dupont with their condos and 2-3 storey rowhouses/semis being able to accommodate a large number of young talent, and North Toronto, The Beaches, The Kingsway putting the executive class also within close proximity. The more close in nodes are still accessible to the same neighbourhoods, but some of the more distant nodes will have to attract young professionals because those mostly like in Old Toronto atm. The lower income workers serving the higher income demographics will also have to be taken into account. I think the ones working in/near downtown are already being pushed out into Central Scarborough and Jane-Lawrence/West/Downsview afaik, which is pretty far out, especially if they're taking TTC rather than the faster GO trains. So there will need to be enough housing built within a reasonable commuting distance of DT Toronto that existing housing can "filter down".
Also, Toronto will have to really make the most of its transportation assets because we're always going to be playing catch-up when it comes to expanding them. Fortunately, getting development to happen is mostly just a case of zoning for it because the demand is there. The one advantage Toronto has over Paris and other older cities is that it can build to higher densities right at the rapid transit stations than 19th century development ever could, so it should make use of that. And to provide opportunities for affordable market housing, townhouses and woodframe apartments should be allowed in much of the bungalow belt.