"pre-French" encompasses a very long time period, and so the feasibility would vary over time.
I wrote a little bit about Swahili settlement on Madagascar in the period from 1000-1500 in this thread.
That answer also mentions the oral histories of the Zafiraminia and Antemoro who trace their origins to Arabia, migrating to Madagascar between the 13th and 16th centuries. However, Kees Versteegh^1 quotes N. Rajaonarimanana to suggest that these groups instead came from the Muslim population of East Africa. There is also a countervailing view that Islamized Malagasy populations (i.e. the Zafiraminia and Antemoro) come from Muslim populations from Sumatra that crossed the Indian ocean and settled on Madagascar in the 14th century. A genetic study by Capredon et al^2 found that Antemoro populations had "middle eastern" haplogroups on the Y chromosome, but the authors were unable to argue for or against an African or Sumatran origin, due to insufficient data from those two populations.
Moving on to the period after 1500. With the rise of Omani hegemony on the East African coast after 1650, we have better information about a growing slave trade that drew upon slaves from Madagascar to supply the plantation economies in Zanzibar, Mafia islands, Pemba as well as directed to Arabia.
At the same time, there is also greater European trade contact with the southern and western coasts of Madagascar, and the Dutch are bringing slaves to the Cape Colony after 1650^3.
The upshot of all of this trade contact and slave trading is that starting around 1700, the Sakalava state that originates on the South-western coast begins to expand to the north. In many ways, it acts like the slaving kingdoms of West Africa (Asante, Oyo, Dahomey), getting firearms from the Omanis, Swahili and Europeans, and exporting slaves. So, in one sense, Sakalava expansionism required greater degrees of hierarchical control and centralization, and more effective military organization and adoption of firearms.^4 Those factors would seem to make the Sakalava empire more capable to resist any potential invasion by Swahili or mainland African neighbors.
By the end of the 18th century, the Merina kingdom of central highlands, which had been a target of Sakalava aggression and slave-raiding, also began to receive guns. By the 1790s, Merina kings were leading campaigns in Sakalava territory, and in the reign of king Radama I (1810-1828) the Merina kingdom conquered most of the formerly Sakalava lands. By 1840, his widow queen Ranavalona I ruled over about 80% of the island, with independent states only in the south and north-western parts of the island.
During the reign of Ranavalona I, from 1828-1861, the queen expelled British and French missionaries and diplomats from the kingdom, in an effort to preserve traditional Merina ways of life, and to promote economic growth through a policy of autarky.^5 Though European industrialists, missionaries and diplomats would try to intrigue to have her more outward-looking son Radama II replace her on the throne, such plots were not successful until she died a natural death at age 83 in 1861.
So, I would summarize this period by saying that while a Swahili city state the Zanzibar sultanate might have considered invading and establishing a presence on the eastern coast of Madagascar (i.e. outside of Sakalava territory), by the 19th century, Merina unification of much of the island made invasion unfeasable, and Merina strength was enough that they could shut out Europeans from 1835-1861, and Britain and France did not seek to invade.
Of course, I have spoken about potential Swahili invasion, and not about any other East African states. In this period from 1600-1900, these societies were also subjected to slave trading from Europeans, as well as Arab and Swahili traders. Or, in Mozambique these societies were dealing with Portuguese colonization. So, I don't think an invasion of Madagascar was in the cards when other issues were pressing.
1 Arabic in Madagascar pdf warning
2 Tracing Arab-Islamic Inheritance in Madagascar by Melanie Capredon et al. pp 13. Pdf warning.
4 Berg, Gerald M. "The Sacred Musket. Tactics, Technology, and Power in Eighteenth-Century Madagascar." Comparative Studies in Society and History 27, no. 2 (1985): 261-79. http://www.jstor.org/stable/178494.
5 Campbell, Gwyn. "The Adoption of Autarky in Imperial Madagascar, 1820-1835." The Journal of African History 28, no. 3 (1987): 395-411. http://www.jstor.org/stable/182192.