Canon calls it "Monochrome" on page 93 of the user's manual for a reason, but notes you can adjust the Contrast, which is covered on page 92.
However, as PJL notes, you have even more control over the contrast if you shoot a Raw file and then use one of any of several methods to then convert the color image to B&W, post process.
I prefer to use a Photoshop B&W adjustment layer, because that gives me the opportunity to control the density of 6 color ranges - 3 of them additive colors and 3 of them subtractive colors.
Plus, I can then diodge and burn and take care of the mistakes God made....See my siggy. ↓ ↓ ↓ ↓ ↓