Longevity is most strongly influenced by proper (or improper) processing. Complete fixing and complete washing are very important to longevity, and then of course using the proper mounting and storage materials. UV light will certainly hurt a silver-gelatin image over time, but properly processed and on good paper (I wonder about the canvas??) it should last a long time; hopefully more than 50+ years, maybe a lot more. Selenium toning will boost the light-fastness even further and is considered very archival.