If they swipe your e-passport, they read out the chip. This contains a digital image of you, all the details that are printed as well and some countries already added fingerprints in them.
A big controversy, since the governments think it raises the security for false passports, but in fact you won't be noticed with a well-made fake passport anymore (because the government thinks it's impossible to make a good fake passport).
What else might show up? Maybe your document ID is logged and will show up recent entries to Canada on the same passport and anything else that Canadian authorities use your passport number for. So basicly: every time you used your passport, they might have made a log note on it. If your criminal history is commited outside of Canada and you never mentioned it to any embassy, it's unlikely that it will show up, since (as far as I know) it's not legal yet for countries to openly share criminal records. Only in special cases international warrants can be sent or specific records might be requested. (Although governments are currently working on making this more accessible for each other.)
I'm not an expert on this, this is what I read through time.