The terrestrial carbon cycle’s response to climate change and rising CO₂ can either mitigate or exacerbate warming, and depends partly on nitrogen dynamics: CO₂ fertilization boosts productivity but may induce progressive nitrogen limitation, which warming-driven increases in nitrogen mineralization can partially relieve. Terrestrial biosphere models with coupled carbon-nitrogen cycles can disentangle the evolving balance between such processes. Understanding C-N system response in Canada is of particular interest, given that Canadian forests are believed to have been net carbon sinks historically (i.e.,1850 – present) and to comprise a significant portion of the global land carbon sink today. Yet increasing occurrence of fire-conducive weather and higher respiration make the future of Canada’s sink uncertain. We use the CLASSIC (Canadian Land Surface Scheme Including Biogeochemical Cycles) model with and without coupled C-N cycles to project Canadian ecosystem responses to rising CO₂ and climate change under fixed land cover fraction for three different socioeconomic pathways (1-2.6, 3-7.0, and 5-8.5) through 2100. Nitrogen coupling significantly affects projections of net biosphere productivity, producing divergent, vegetation-specific responses to CO₂ fertilization and nitrogen availability. Evergreen species currently dominating Canadian boreal forests show enhanced productivity that sustains Canada’s land carbon sink, even as boreal fire emissions intensify, while broadleaf species experience increasing nitrogen limitation. Canada can remain a net carbon sink, but faces rising wildfire emissions.