This is our standard studio scene comparison shot taken from exactly the same tripod position. Lighting: daylight simulation, >98% CRI. Crops are 100%. Ambient temperature was approximately 22°C (~72°F).
Nikon D90 vs. Canon 450D (Default)
Nikon D90: Nikkor 50 mm F1.8 lens, Aperture Priority, ISO 200
JPEG Large/Fine, Manual WB, Default Parameters (Standard), Active D-Lighting off) Self-Timer (with delayed exposure)
Canon 450D: Canon 50 mm F1.8 lens, Aperture Priority, ISO 100
JPEG Large/Fine, Manual WB, Default Parameters (Normal), Self-Timer
4.6 MB JPEG (4288 x 2848)
3.7 MB JPEG (4272 x 2848)
As we saw with the comparison to the D80 (itself not the sharpest camera in the cupboard), the D90's default output is very soft, having had very low levels of sharpening applied. Canon, meanwhile, takes the opposite approach, delivering very crisp (and contrasty) images at its default setting. Other than that, there's little to choose between the two. Comparing the two in RAW will show how much underlying difference there is, once you scrape away the manufacturers' image processing decisions.