Egypt rental.. well
You may be able to book rides to the Black and the White deserts from Al-Bahareya (400 km SW of Cairo), there is a guy called Amin at Peters' hotel organizing overnight desert tours on Suzukis DRZ400 in good conditions.
There's also a possibility to rent a KTMs in Sharm El-Sheikh (though rather old bikes from my observation of last year), pls ktmegyptcallingdakar - desert tour*Sharm*el*Sheikh*/*KTM bikes*for hire
The owner is trying to revitalize the business in trying circumstances. Renting KTM bikes for a few hours is expensive but they provide all the gear. No overnight expeditions at the latest news.
Apart from that, there's this guy offering tours, never seen or tried but he seems serious: Long Range Travel
Harley Davidson Egypt (Mohandissen and Zamalek) does not rent bikes, unfortunately.
But are you sure you want to ride a bike in Egypt, even in Cairo? Unless you come specifically for desert riding, I'd recommend renting a car, it's by all means safer, more comfortable in the heat and convenient on highways between points of interest. Just don't forget your driving skills at home!
Scuba diving: Marsa Alam is apparently not yet damaged.