I'd say there is certainly an element of truth in both points, but only as long as the plans are understood as part of a far broader attempt to modernise the city in different ways. In this sense, military concerns weren't the only reason for the program, but rebellion was one of a number of perceived social ills which Paris' modernisation was designed to combat.

Nineteenth century France had a highly turbulent political atmosphere, not only due to the aftermath and legacies of the 1789 Revolution but also due to a number of major rebellions. Between 1830 and 1848, Paris saw six armed uprisings, so it would not be unsurprising that there might be a desire for better crowd control. However, in 1870-1 there was another uprising, known as the "Paris Commune", which Rougerie argues was easily suppressed because the army vastly outnumbered the Communards, and not because of the boulevards (2014: 115) Interestingly, de Moncan argues that Hausmann may have exaggerated the military purposes of the urban renewal programme to make it more attractive to Parliament (2012: 34). In short, the urban renewal plan was thought of by some as a means to achieve easier crowd control, but it wasn't very effective.

However, to think of "Haussmanisation" only in these terms is to oversimplify it. Urban modernisation plans in the nineteenth and early twentieth centuries across the globe responded to a range of perceived social ills or pathologies which were deemed to be holding the nation / society back. These social ills often included (but were not limited to): poverty, disease, alcoholism, prostitution, and political radicalism. Michel Foucault argues (not without criticism) that modernising trends responded to the "haunting memory of ‘contagions’, of the plague, of rebellions" (1997: 198) and that modern states developed a number of mechanisms and techniques for ridding society of these ills. This kind of plan was by no means to Haussman's Paris, and Leif Jerram's book 'Streetlife' (2011) is a particularly good account of how these trends have continued in the twentieth century.

So whilst, yes, Hausmann's reorganisation was perhaps partly motivated by the potential for greater crowd control, it was more deeply influenced by an attitude which believed that state intervention into public space was necessary to modernise the city, and in doing so modernise society. So, alongside the new boulevards, Hausmann was also responsible for the building of new sewers, parks, and public buildings such as hospitals and schools, which it was believed would help to foster a modern society.

His overall goal was therefore to use urban renewal as a means for tackling a whole range of issues, of which rebellion was certainly one.

Burton, Richard DE. Blood in the City: Violence and Revelation in Paris, 1789-1945 (2001).

de Moncan, Patrice. Le Paris d'Haussmann (2012).

Foucault, Michel. Discipline and Punish: The Birth of the Prison (1997).

Jerram, Leif. Streetlife: The untold history of Europe's twentieth century (2011).

Rougerie, Jacques. La Commune de 1871 (2014).

Sweeny, Niamh. Haussmannization and the Conquest of Place: Configuring Parisian Global Influence on the Second Empire (1852–1870) (2008).

Related question- I had always heard that it was designed with wider streets to make it harder to build streetwide barricades. Is there any truth to this?