Yes because in our timeline France had a huge fertility drop in the late 18th century. The whole basis of this POD is that does not happen and France's population around 1900 is not 40 million but over 100 million. That makes metropolitan France much more crowded, pushing up land prices, making it less attractive to live, and encouraging immigration.
100 million was
never specified in the first post of this thread. "Tens of millions", yes, but how many tens of millions?
(I would also suggest putting slow French population growth down to patterns of land inheritance misses the point somewhat. Why is land scarcity supposed to be less effective incentive for population control than, well, land scarcity?)
At any rate, simply having a high rate of population growth nationally does not at all mean that a particular territory under the authority of that country will end up being resettled. Look to France's east, in Germany, where the eastern provinces remained recalcitrantly Polish. Why did this happen, when
belle époque Germany's population nearly doubled? Put simply, Germany did not want to settle in substantial numbers as farmers in the Polish provinces, migrants preferring German cities or overseas destinations. (That emigration is what people in the Polish provinces did, for that matter.)
A France with relatively high rates of population growth is likely to be a source of more emigration, but why is Algeria likely to be preferred? Why not Argentina and Uruguay, or the United States, or Canada, places offering relatively high wages in a familiar setting? Why Algeria?
The cheap labour and cheap immigration do not contradict each other, as we see in places like South Africa over the last 150 years.
It does. The inexpensiveness of African labourers, already present in South Africa by the millions, prevented South Africa from developing along the lines of Canada or Argentina, with an overwhelmingly white population occupying every different niche in the economy and natives being shut out. Instead, it became a place where African labour was always present. This prevented the country from being a particularly attractive destination for unskilled labourers.
Why did South Africa attract immigrants anyway? It was not agriculture, but rather the wealth associated with its abundant mineral riches, wealth which supported the construction of an urban-industrial economy. It did manage to attract skilled migrants, and still does.
Algeria lacks this natural abundance, its oil only starting to be exploited
in the 1950s and its other resources not being found in the fabulous abundance of, say, gold in the Rand. Without this, where is the incentive for migrants?
Even before apartheid, people could buy up cheap land even outside areas of population clearing. That's especially the case where rural land adjacent to a city is converted to urban homes. You don't need the local population kicked out the country, or even moved districts (though that is plausible and not out the norm for colonial powers). Their incomes are so much lower, they can be bought out.
This sort of thing
happened in our history, too. Even then, and even with rapid population growth on the northern rim of the Mediterranean that was the source for new European immigrants to Algeria, the immigrant proportion never got above 15% and was 1%.
Yes, you would need to move beyond a planter agricultural class, but you can just do more urban cities becoming French.
Even that is going to take many more immigrants than is practicable, especially when the rapid growth of Algerian Muslims--something that dates to the 1870s--is taken into account. The example of Oran (
French-language Wikipedia), a city that went from being more than 85% European in 1921 to two-thirds European on the eve of independence, thanks to migrants, is indicative. There are just too many Algerian Muslims for Algeria's major cities to not end up overwhelmingly non-European. Even if all the pieds noirs had stayed in the early 1960s, they would make up only 3-4% of the population. Even if their numbers had doubled--how? why?--they would barely breach the 5% mark.