The 7D Mk2 will be two years old in the autumn, so a replacement is a possibilty if it keeps to the old XXD release schedule. If this is the case, then I'm sure that Canon will already have it well under development, so while the earthquake/tsunami may delay production lines and tooling up, I don't think that they'd pull an anouncement completely. More likely they would announce in early autumn with delayed shipping until the end of the year (I'm sure they'd want to get some stock on the shelves for Christmas). The question is more, is the 7D on the old XXD release schedule, or does Canon consider it a "professional" model on a 3 year cycle? So, if this is the case (and this rumour is true), what else could a third DSLR be?
Allow me to indulge in some speculation (hey, this is a rumours site!):
I doubt we'll see a new Rebel, as both the 550D and 1000D have been updated this year. I guess that something completely new, such as a smaller model to compete (I hate that term) with mirrorless cameras, is a possiblity; where it would be positioned, spec wise is anyone's guess. The other option might be a "pellicle" mirror type camera with an EVF, which Canon must have numerous patents for.
If the new 1D line model is to be a 1Ds Mk4 (i.e. if the rumors of a merging of the 1D and 1Ds lines are false), then a third DSLR release could be a 1D Mk4N; Canon have done a mid-life update like this before with the 1D Mk2N. This might share a lower resolution sensor with the 5D Mk3, but have a faster continuous shooting rate etc. I'm suspecting that Canon might offer something like this, as they seem to have gone to great lengths to lighten the weight of the 400mm F/2.8L; just the lens that a sports shooter moving from an APS-H sensor 1D +300mm f/2.8L to FF would need to maintain the same angle of view.
Of course, this is probably all rubbish and we'll see 'just' a 40MP+ 1Ds Mk4 and a 28-32 MP 5D Mk 3 this year (if we're lucky).