It's not messing up anything. So, I don't have a "Big" complaint by any means since my prints are turning out well. It just bugs me a little.
On my Pro9000, it was a useful tool. I'd had a lot of trouble turning off color management in the printer, so I was running with colors "managed by printer". In that mode (and with OEM ink) if the preview picture matched my LR picture, the print would turn out well. If it didn't match, the print would be bad. So I got in the habit of checking it. I guess we can conclude that the Canon "printer preview" doesn't incorporate any externally applied color management - even if you're using a Canon-built profile.
Is it worth trying the Canon "Studio Plug in" that's supposed to work inside LR?