You can load "trips" from Basecamp to recent Nuvis, no routes, neither tracks (no Nuvi can import tracks).
You can load routes from Mapsource to nuvi 1450/90.
All of the newer models have limited compatibility with computer route planning because they have switched to something called "trips", but old 1400 series can use classic Garmin "routes".
You need to import the routes once Basecamp has sent them to your nuvi. Go to Tools>My data on 14xx and select Import Routes.