Highly pathogenic avian influenza clade 2.3.4.4b H5Nx viruses (HPAIVs) have caused significant mortality in wild birds. We investigated active avian influenza virus (AIV) infections and assessed seroprevalence based on general nucleoprotein-specific and H5-specific antibodies, in seabirds in Atlantic Canada during 2022-2023. Results were compared to seroprevalence data from 2011-2016 to evaluate changes in infection rates following the incursion of HPAIV. We sampled 1073 wild live birds belonging to 14 species. Active H5Nx infections were detected only in 2022, with the highest prevalence in Common Murres (64%), followed by Black-legged Kittiwakes (13%). Differences in seroprevalence were observed between years and species, with both Common Murres and Atlantic Puffins exhibiting higher rates after HPAIV incursion, particularly for anti-H5-specific antibodies. Seroprevalence also differed between locations, and age-related differences in exposure were observed with juvenile birds having much lower seroprevalence than adult birds, particularly among gulls. Despite no active infections being detected in 2023, high seroprevalence across species suggests persisting immunity and/or recent virus circulation. These findings underscore the importance of serological monitoring in tracking AIV dynamics, as antibody detection provides critical insights into past HPAIV exposure even when active infection rates are low.