True, the Bible does not say the title of the post (substitute 'Jerusalem' for 'Cairo' and it does, Psalm 122:6), but these days it is just about the same thing, because should Cairo fall into the wrong hands viz a viz the complexity of life, politics, and all that in Palestine/Israel, then the peace of Jerusalem will be imperilled.
I imagine life for Anglicans in Egypt is challenging through these days. As citizens of Egypt they will aspire for good democratic, just government with their fellow citizens; but as realists they will know that should the government of Mubarak topple then it is possible that its replacement (or, eventual replacement) will be an Islamist government. Life is tough enough for Christians in Egypt under the moderate (in respect of religion) government of Mubarak - occasional bombings, lots of subtle and not so subtle anti-Christian pressures (e.g.) restricting church activities and constraining career aspirations of Christian professionals - tougher would be an Islamist government. So praying for the peace of Cairo (the key to Egypt) is praying for a settled state of civic life in which Christians are treated justly, with equal freedom and opportunity as enjoyed by Muslims.
(Bio note: I lived in Cairo, 1982-83, not long after Mubarak began his rule. That vast and populous city was incredibly friendly and safe to reside in. But part of the reasons for feeling safe were the visible signs of military dominated rule: soldiers guarding many buildings. But there were other signs of that dominance such as friendly warnings to take care with what one said because the secret police were anywhere and everywhere. Life was free yet constricted. Many years later the constrictions are obviously chafing).