I agree with everyone who says take a DSLR. Some of the lower cost (and even higher cost) point and shoots (P&S) can take up to a second to take a picture once you hit the shutter. A DSLR's lag is measured in MILLIseconds.
At night or in low light, there's no way a P&S can match a DSLR--small sensors mean lots of noise. Big sensors mean less noise. Period. Most P&Ss useless at night above 200 ISO. You can get 800 or more WITH HIGHER QUALITY from a DSLR. This means that you don't miss pictures after dark.
Furthermore, DSLRs can be just as easy to use, and, in fact, are frequently MORE forgiving of less than perfect technique.
Canons are great cameras. However, if you look at what the Disney Photopass photographers use (at least last time I was there)--it's Nikon. The quick easy and cheap solution would be a D40 or D60 kit. You can get a D60 with a 18-55 VR lens (handheld nighttime pictures of fireworks at the castle are possible with this!) for about $520 from a REPUTABLE seller. $460 for the D40 without VR. Sure, the DSLR is a little bigger and heavier, but, having run around WDW for 9 days with a heavier camera (D200), trust me, you can handle it.
Ultimately, go somewhere that you can try both out and see what you like better. Comparing Nikon to Canon is like comparing a BMW 530 to a Mercedes E350. Both are really nice, German, midsize luxury/luxury-sport cars. Both have almost the exact same features. Both are about the same size. Both have six-cylinder engines. And both feel completely different and, odds are, one will feel great for you, and one won't. (hopefully I avoided starting a canon vs. nikon war)
One last tip.... Don't worry too much about megapixels. 6mp from a DSLR will frequently outperform 10-12mp from a P&S.