Starting a foreigin Activity/Application is quite easy.
Intent intentHandle = this.getPackageManager().getLaunchIntentForPackage("com.android.browser");
this.startActivity(intentHandle);
But is there any possibility to specify the orientation, the foreign Activity/Application is forced to use?
This depends on the source code of the application. To my knowledge, this is not possible. As Each application can handle orientation change differently or just not do it at all.