Yes. Import the gpx file into Basecamp. A new list will appear in the Collection with the route in it.
Just be aware that the Nuvi will not use the route as it exists in Mapsource/Basecamp. Nuvis always recalculate the route the first time you use the route.
If you have the same maps on the Nuvi and the routing preferences are set the same as the PC programs, the recalculated route should end up the same but no guaranties.
