I can't imagine you'd build one for less than 10,000 AADT, which we've discussed before. Though it's certainly not necessary before 15,000 and that's more likely what I'd expect from MTO unless there's a big push politically.
Looking at the 2021 numbers, it's about 19,000 where the 417 currently ends, dropping to 14,900 at Highway 60 south of Renfrew, which is just before the widening ends. Then just north of Renfrew it's about 14,000 but then not much further at Haley where road to a bridge across the Ottawa River.
From there it oscillates from 7,000 to 10,000 to Deep River, and then falls off the cliff quickly to 3,000 to Mattawa and then steadily picks up from there to about 9,000 when it hits Highway 11.
West of North Bay it's about 9,000 to 10,000 to Sturgeon Falls, where it drops to about 6,500 to 7,500 to Markstay, climbing steadily hitting 10,000 at Nickel Centre, and then rising to about 16,000 when it hits Sudbury's SE Bypass.
The SE Bypass itself is only 11,500 between the old Highway 17 and Highway 69.
To put some perspective though, the 17 expressway from the SW Bypass to Whitefish is only 9,500 dropping to 7,500 where it joins old Highway 17 - but then is a steady 10,000 from there to Espanola (Highway 6). So while the demand on old 17 might well have justified an expressway, a significant amount of traffic is local, and stays on slightly shorter old road.
After Espanola, 17 is as low as 4,000 heading to Sault-St. Marie, and then 1,400 to Highway 11, east of Thunder Bay. Then it's about 2,500 to 3,000 to approaching Manitoba, with a bit higher approaching Dryden and Kenora.
So most of Renfrew to North Bay is a long, long away. My guess would be Sudbury to Nickel Centre. And we'll see Sudbury to Highway 6 done before much of the highway between Renfrew and North Bay.
Looking at other roads, Highway 7 between Guelph and Kitchener, where they are going to build an expressway, is 18,000 to 23,300. Even at Acton it is 15,000 then, 20,000 at Trafalgar Road. Where the Highway 7 expressway around Peterborough ends, it's 26,000 - all the way to Highway 28 - it's 4-lanes of course, but it's absolutely not expressway. Then it's 10,000 to Norwood. Very quiet (less than 4,000 to 5,000) to Perth, and rises then to 12,000 at Carleton Place, near where the expressway ends (22,000 on that new expressway).
The 2-way section of Highway 6 that they are planning to replace with expressway from Puslinch to the 401 is 25,000 to 29,000! That's insane for a 2-lane road!
This is the 2021 data from
https://www.library.mto.gov.on.ca/SydneyPLUS/TechPubs/Portal/tp/tvSplash.aspx