In this paper, we analyze the evolution of the expert discourse in the media during the first wave of the Covid-19 pandemic in Canada. From our analysis of 527 media products published by CBC/Radio Canada between January 1 and August 31, 2020, it was possible to document the type of expertise mobilized, the types of experts engaged by the media, the modalities of appropriation of this discourse by non-experts and the use of expert discourse by political actors. We organize our analysis around governmental measures that have generated more controversy and debate in the media (e.g., closing international borders) and that will be used to analyze the processes of representational naturalization (Negura and Plante, submitted). We begin our chapter with an overview of the use of expertise in the Canadian public- health decision-making chain in the context of the Covid-19 pandemic by highlighting the tensions, contradictions, and paradoxes in political communication that this process revealed. We demonstrate the relevance of studying these dynamics reflected in the media from the perspective of social representations. A brief explanation of the research objectives, the data used and some methodological elements will follow. We then discuss the results of our analysis of the different stages of the evolution of the pandemic in Canada according to the expert discourse in the media. Finally, our analysis focuses on the role of expert discourse in determining what aspects of Covid-19 the public and the political authorities in Canada have defined as a social problem.