Contrast ratio is the ratio of intensity between the darkest point the display can make and the brightest. In a dark room, the bright white spot will be 1000 times brighter than the blackest pixel on the 1000:1 ratio or 900 times on the 900:1. From that stat alone, the Epson has an advantage, however that also isn't the only stat you need to look at.

Maximum brightness (Lumen output for projectors) is also critically important. It is quite typical for brighter projectors to have a lower contrast ratio since preventing light leakage becomes harder as brightness increases. The lumen output of a projector determines how bright an image can appear and what kind of brightness the projector could be used in.

For example, if the Epson was a 1000 lumen projector and the Canon was 5000 lumen (hypothetical, I'm not looking at their stats), then while the Epson may win in a dark room, in a well lit room, the Canon's brightest pixels would be much brighter than the pixels lit by ambient light and thus the effective contrast ratio for the Canon would be higher in a well lit room since it would stand out more from the ambient light level.

There is also a question of the color accuracy of the projectors which is difficult to measure from most stat sheets. Color accuracy is a trick with projectors in general since ambient light impacts them so strongly, but just like other types of displays, not all projectors are created equally in relation to how well they can reproduce color.

So to sum it up, the main things you want to consider when looking for a projector for photography are generally going to be the contrast ratio for the condition you will be using it in, the ability to reproduce color well and then finally the resolution of the projector.