The French would have had to made major adjustments to their colonial policy: granting more land to settlers rather than the "seignors" which acted as landlords and offering additional liberties.
Allowing protestants to settle there and subsidizing transport would have gone a long way. If French Canada had possessed another 100,000 people, I question if it would have been conquered in 1759.
Not only that, but the French government in general didn't care much to promote emigration to New France. Some within the government (including Colbert) even argued against it, claiming that France was underpopulated. The government made some effort to recruit colonists in 1663 (when it became a royal colony) but this largely ended in 1672 with the outbreak of the Dutch War.
The effects of that one decade of recruitment can be seen in the
spike in New France's population from 1666 to 1676, when it grew from 3,215 to 8,415 - a 162% increase. But over the next decade growth slowed to 47%, to 12,373, as the growth was now fueled almost entirely by natural increase. Growth thereafter would be relatively modest.
If the Dutch War could have been delayed or avoided, or Louis XIV's government simply taken more interest in recruiting colonists from the 1670s onward, the population could have quite a bit larger by the mid-18th century.