Agree with Mijael Feldman Sabah, don't do it. Focus on one country first. Even if you are very rich, and you can cover investments in both countries, the traction will be much faster if you focus on one market. Your resources will also get a better ROI if you can focus.
Selecting one market over the other should depend on your business model and where it has the highest chances to succeed - for that, you might be interested in Customer Seduction, a simple yet proven business model course I've created on serenademaio.com
Good luck!