Hi,
If you choose the D-Rebel and you want TTL you will have to select your housing and strobes very carefully. The 100a will not do TTL with the D-Rebel. Aquatica has developed a special TTL conversion circuit for use with the D-Rebel, but it only works with the new Ikelite digital strobes and Sea and Sea strobes at present. More strobes will probably come along that work, but the 'ol 100a doesn't recycle fast enough (I could be mistaken, check w/ Aquatica).
If you don't need TTL, you can shoot your 100a's in manual with just about any camera and housing, but you won't get much strobe control w/ only a few settings on the 100a's. There are a variety of housings available for this camera, such as Ikelite, Aquatica, Sea and Sea, and UK-Germany.
On the other hand, if you are set on keeping your 100a's, you can use them in TTL with the Fuji S2pro. It is a bigger setup than the D-Rebel though. I would look at the total cost of a DSLR system, first a D-Rebel+housing+new strobes. Then compare to the Fuji S2pro+housing.
Cheers
James