Newfoundland and Labrador will never agree to a split. Quebec wouldn't agree to splitting off any of its land (Gatineau for a NCT) or its far north.
There's a potential case for Northern Ontario, but your boundary is very arbitrary. The whole north - all the way from North Bay to Kenora would fit better, and there's a lot of resentment in Northeastern Ontario over ONTC, parks closures, and other slights.
Labrador and Newfoundland are not even connected by land, and to me it looked like they could become very interesting regions with slightly different characters and landscapes in Canada. But I guess Labrador should be on its own as a great land of Labradorian only after Quebec's separatism and the ambition of claiming southern part of Labrador as part of Quebec is relinquished.
Nunavik, currently in northern Quebec, has more than 90% of its population as Innuits. It was surprising how media almost reported nothing about it when it happened back then, but Nunavik have already had a referendum in 2011 to create self-governing territory whose borderlines shown on the map(above). Majority of Nunavik people were asked to vote No as the referendum date came closer because of some important reasons. I believe the condition that clearly says it will become "a territory within the province of Quebec" was not what they're ultimately looking for when Nunavut was able to have their own government with the recognized status of "Territory" in the country. Also, if I must say, Nunavik is strongly against separation of Quebec from Canada. Federal government could have planned/informed them to stay in Quebec, for now.
Northern Ontario- I'm not a politician nor an expert on the domestic issue there except that there are also some group of native people in north west region of Ontario. North Ontario with that border is going to have the same diagonal width as Manitoba. It is very proportional in that way from British Columbia all the way to North Ontario, thus looks balanced and beautiful. This work has been already done when you see current map of Canada west of Ontario. I'm merely perfecting or completing the art of it. The population of Northern Ontario with that borderline will have population of approx. 500,000. - If I'm the president/prime minister of Canada, the creation of the Province of North Ontario should be accompanied by a plan to make its population reach 1 mil. or similar to the one of Manitoba.
In terms of landmass, the remaining Ontario, with that lightning shape, will still have the access to Hudson Bay(James Bay) and will not be significantly smaller than Quebec minus Nunavik.
Lastly, the National Capital Region - It is biased when the capital city of the federation belongs to 1 of the many provinces in the country. The capital of a large federation like Canada, US, Australia should have a dedicated Capital Territory which is neutral and strong. You said the regions on Quebec side will not agree on this. Well, tell them they won't be obligated to pay the notorious provincial taxes any more, instead they will get more benefits as citizens of the National Capital Region.
Again, my main focus on creation of new provinces and territories was to make Canada's (political) map make more sense and look balanced. And don't say "never". Even the Greater Montreal Region could become a new province of Canada to resurrect itself from being a victim of Quebec's provincial politics for so long.