For questions like this, Forvo is a good resource: http://forvo.com/word/monday/ http://forvo.com/word/sunday/#en Keep in mind that in English, we usually use "u" to represent the sound usually represented by "a" in other European languages ("a" usually makes us think of the vowel from "cat"), so Monday and Sunday would be pronounced [sundei] and [mundei] respectively. In IPA these would be /ˈmʌndeɪ/ and /ˈsʌndeɪ/.

Both are acceptable. 'mʌndi is more informal and not everyone says it (I don't). If you're aiming for a professional sounding accent, then I recommend -deɪ

According to the Longman Dictionary of Contemporary English (I just checked minutes ago), either pronunciation is possible with each of the seven days of the week in British English: Sunday /'sʌndi, -deɪ/, Monday /'mʌndi, -deɪ/, etc.

scottish - Mandi american - Mondei