Here are some ways you could say it, depending on the context:
Informal:
* Hey, bro!
* What's up, dude?
* How's it going, man?
* Yo, what's up?
More formal:
* Hello, brother.
* Good to see you.
* How are you doing?
The best way to say "sup bother" depends on the relationship you have with the person you're talking to and the situation.