France's population was essentially stagnant from 1870 to 1914 and there is no indication that avoiding WW1 would lead to a population boom or significantly greater population growth in France for the remainder of the 20th century. Therefore I'm not sure where this "much larger population" will be coming from ...France is a great candidate, IF they the avoid walloping of WWI (and preferably the Franco-Prussian War as well, but that's too early a POD). For most of European history, France was the largest power in Europe, with more land, men, and wealth than any other. That's why France was historically able to do insane things like essentially uniting Europe under Charlemagne, seizing the Papacy, or facing the whole of Europe on its own after the French Revolution. There is no doubt that Britain was much more powerful than France in the 19th century, but even then France was still clearly more powerful on the continent itself. And with a much larger population and being perhaps more advanced than other powers in aircraft and tank design, France was on track to having a good 20th century before WWI.
Then again, perhaps any major European power that sits-out WWI is on track to become a super-power.
France also had significant economic challenges in the early 20th century with an archaic agriculture that sucked half of the workforce and an industrial sector that wasn't on par with its rivals.
A lot of France's challenges were only solved after OTL's WW2 and the utter shock of being defeated by Germany which provided impetus for significant reforms, strengthening the state, institutions etc.
To become significantly more powerful than OTL, France needs a bigger population and an even stronger economy than OTL, one that is world-leading in key sectors.
France's sub-Saharan colonies were frankly more a hindrance than an asset to France during the 20th century. They fostered protectionist feelings in some industrial sectors and needed significantly more investments in order to become profitable and self-supporting parts of a 'Greater France'.If we really want to say "Continental European" then France is your man: industrialized, militarized, prestigious and a center of arts and culture, if France manages somwhow to avoid the devastation of WWI maybe fighting the war on German soil, or survive the Blitzkrieg in 1940, it won't incour in the national humiliation and devastation that followed the war, being able to bounce back rather quickly thanks to it's massive colonial empire. But alas, France has a much smaller population than the British empire and even avoiding millions of dead men (who are unable to make children) during WWI, a tight grip on Africa would be necessary: expect decolonization to be much slower and France retaining massive control over it's former Subsaharian colonies for their resources, needed to fuel the French industry at low costs.
In order to become profitable and able to stand on their own, significant investments would be required. The most challenging of which would be investing in the local people themselves through education, healthcare, social services etc. In effect 'software' as opposed to 'hardware'.
Theoretically one way to make France a superpower over the course of the 20th century is a 'Greater France' scenario or the "France from the Rhine to the Congo" advocated by some as late as the 1950s. In effect this means integrating the entirety of North+West Africa within the country and making it part of the metropole over the course of the century.
What does this involve, well let's start listing the theoretical requirements in a cold blooded pragmatic way shall we:
1. A very strong assimilationist/inclusivist attitude from the French state to turn Africans into Frenchmen over the course of the century.
2. In order for 1. to happen successfully, racism and racialism must have no place within France and the French consciousness.
Considering OTL's code de l'indigénat, the lack of suffrage in French Algeria until it was too late etc. I think that we can stop here, but let's continue shall we?
3. Building schools, hospitals and a state infrastructure all over France and its overseas territories. This means building tens of thousands of schools, thousands of hospitals and eventually training millions of civil servants to operate them.
4. Building asphalted roads and railways all over the African territories, potentially >100,000km for the roads alone. Said territories have population densities are lower than metropolitan France so the infrastructure may not be profitable initially and will likely need to be subsidised.
5. Upgrading African agriculture with access to irrigation etc.
6. Significant investments in natural resources extraction in the overseas territories.
7. Building-up industrial centres in overseas France and training (or importing) a workforce to operate them.
For this one, I doubt that industrialists from metropolitan France will be happy to see new industries propping up in what were previously carefully protected markets.
8. A booming economy able to generate huge profits and surpluses available to invests to make points 3, 4, 5, 6 and 7 possible.
Considering all the constraints outlined above. In my opinion, this 'Greater France' scenario is almost impossible to achieve.