You'll see a list of routes. You can transfer the list to the device memory and it will offer to import the routes when you switch the device on (at least that's what the 220, 550 and Nav V do) As belt and braces you can export the GPX file of the routes onto the SD card in a folder called /Garmin/GPX. You should then be able to import the routes by going to 'My Data' or something like that (each machine has slightly different user interface). When it imports routes from a GPX file, you'll see a list of all the routes within that file.
Try it, it only takes a moment to check how it works.