Well, if he's refused for criminality, appealing wouldn't help much anyway. :/
As far as his past mistakes:
1) Canada won't care about his illegal crossing because if he's a PR, it won't happen anymore. They also don't care about overstays either. The only time CIC cares is if you apply for temporary status. Since PR is permanent, it won't matter much.
2) The conviction - is the crime he committed worth 10 years in Canadian jail? Or against a family member (I. e., domestic assault)? Those are the only two things I would be seriously worried about. (Unless he was a warlord or ran a criminal empire, but I think he'd get more than 3 months for that....
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The good news is - IF there are questions, CIC will contact you first. If there is something on his record, they will ask for an explanation if they need one. If they aren't certain of your genuine relationship, they will call an interview. They will give you a chance to prepared and address their concerns. In that aspect, CIC is quite fair. IF something does happen, then you order case notes: http://www.cic.gc.ca/english/department/atip/requests-atip.asp
But don't worry about it right now. And I agree with you about the kids - but hey, some women here get pregnant by a "rich" guy just to get his child support... so having kids for the wrong reasons happens all over the world :/ My husband has a good job and he's had to run away from a few that wanted to have his baby right away, but weren't interested in getting a job....