Hi grostoutou, welcome to GPSPower.net!
Please note the nüvi 350 is limited to recognizing map files up to 2 GB only. Depending on which map you refer to, you may need to download the PC installable version (AKA MapSource version) and create a custom version of the map using MapInstall, selecting only those map areas which you are interested in, not exceeding the 2 GB size limit. Noting your location is Canada, it's my guess you're using the CN North America. The size of the 2014.30 version was 1.97 GB. As of the 2014.40 version, the 2 GB mark was exceeded. The latest version 2017.20 measures 2.58 GB.