This is your brother. Is your rel@tionship more formal that you have to dance around pleasantries and can't simply say you were hurt?
"You know, Bro, you cancelled on my birthday dinner, and then ignored me when I texted you to reschedule, and I'm hurt. What's going on?"
I wouldn't text, I wouldn't email, I would call and have a conversation.
Or I would just ignore the whole situation and plan to get together and let this one go.
You say this is pretty typical for your brother. Have you (or anyone) tried to redirect and correct this behavior, or does everyone just accept this as the standard norm? I think it's worth pointing out his actions to him so that he can make some changes, maybe he doesn't know or understand how is actions affect people, but this could also very easily cause an argument and division, so you might have to let this one go. This wouldn't be my hill to die on.
Facebook post: Yes, let's get together, what time is good for you?