Canon is on a different fiscal year than Nikon, and they've already reported their first quarter results for 2010. This gives us some numbers to compare against next week's Nikon numbers.
Short version: on a year-to-year basis, Canon sold 11% more cameras in the first quarter of 2010 than 2009. 19% of those cameras were DSLRs, and DSLRs represent 62% of Canon's revenue in cameras. Canon also increased their projection for camera sales for the entire fiscal year from their estimates one quarter ago. (Canon does not report specific unit volume breakouts as does Nikon.) From their report: "...demand for digital single-lens reflex (SLR) cameras displayed solid growth throughout global markets, whereas demand for compact digital cameras maintained growth in emerging markets, such as those in Asia, but remained relatively sluggish in developed countries." Canon specifically pointed out growth in sales of the T1i, T2i, 5DII, and 7D cameras.
The question is whether Nikon matched that growth. Note that the specific cameras Canon mentioned as having significant growth are basically equivalent to the Nikon D3000, D5000/D90, D300s, and D700. I don't think Nikon had solid D3000 or D5000 sales during this period, and the D300s and D700 have needed price drops to keep volume moving. Early whisper numbers out of Japan say that Nikon increased DSLR unit volume over their estimates, but I don't think this came easily for Nikon. Moreover, it's still unclear how Nikon will top their just finished fiscal year in the coming year. At least three, and probably four, of those key cameras need replacing with substantially better products to remain competitive, in my opinion (D3000, D5000, D90,and D700). It's been six months since Nikon introduced a new DSLR, and that was a high-end one. We're nine months removed from the last non-pro DSLR announcement. And we still don't know what Nikon's responses to the S90, G11, E-P1, E-P2, E-PL1, G1, G1H, GF1, G2, G10, NEX3, NEX5, NX-10, or X1 is going to be. So Nikon users are nervous.