We're about 6-12 months away from finding out how Qantas' latest challenge to Airbus and Boeing has gone. "Project sunrise" was a challenge to the big aircraft manufacturers to design a plane that could economically fly 250-300 people across 3-4 classes from Melbourne & Sydney non-stop to London and New York.
The longest of those sectors is Sydney-London (9,188 nautical miles, v 9,127nm for Melbourne-London). Melbourne-New York is the next longest sector (9,015nm versus 8,646nm for Sydney-New York) however, there's been no mention of Toronto which arguably should be on the cards at least in the medium term if the aircraft manufacturers can produce a plane that will be able to do what Qantas is asking for. It appears it's a competition between potential variants of the A350-1000 or B777X.
Melbourne-Toronto (MEL-YYZ) on great circle is 8,774nm (versus 9,015nm MEL-JFK above) and Sydney-Toronto (SYD-YYZ) is 8,397nm (versus 8,646nm SYD-JFK above). It goes without saying, if the planes will be able to make the trip to New York from Melbourne/Sydney, they'll be able to make it to Toronto.
The Australia-Canada bilateral was liberalised not long ago (there were silly old-school restrictions like only able to choose a max of two different ports in each respective country - it was removed so that AC is now free to fly YVR-SYD/BNE/MEL - and they're now doing that) and Qantas codeshares with Westjet. I dare say beefing up numbers on the main long-haul sectors won't be that much of an issue with Westjet feed being really good eastwards from Toronto to/from Ottawa, Montréal, Québec City and Halifax.
Yep 20 hours in economy would suck, but Qantas' Perth-London flight (17.5 hours) on a 787 is going great guns apparently and there's been talk of introducing common areas into the internal configuration for economy passengers on the project sunrise planes. If you don't want to fly Air Canada at the moment, to get from Austrlaia to Canada, excluding QF's seasonal SYD-YVR flight, you have to go via the US, NZ or a much longer pacific circle route (i.e AU-HKG-CA on Cathay).
The only other city mentioned as part of project sunrise is Paris/CDG but I wouldn't be surprised if Toronto gets a look in eventually as Qantas have barely any presence in Canada - this might be their avenue in (leaving AC alone on Vancouver-Australia routes).