How to externally populate a Django model?
I've used cron to update my DB using both a script and a view.  From cron's point of view it doesn't really matter which one you choose.  As you've noted, though, it's hard to beat the simplicity of firing up a browser and hitting a URL if you ever want to update at a non-scheduled interval.
If you go the view route, it might be worth considering a view that accepts the XML file itself via an HTTP POST.  If that makes sense for your data (you don't give much information about that XML file), it would still work from cron, but could also accept an upload from a browser -- potentially letting the person who produces the XML file update the DB by themselves.  That's a big win if you're not the one making the XML file, which is usually the case in my experience.
What is the best idea to fill up data into a Django model from an external source?
E.g. I have a model Run, and runs data in an XML file, which changes weekly.
Should I create a view and call that view URL from a curl cronjob (with the advantage that that data can be read anytime, not only when the cronjob runs), or create a python script and install that script as a cron (with DJANGO _SETTINGS _MODULE variable setup before executing the script)?