From CIC:
"You may not be eligible to be a sponsor if you:
* failed to provide financial support you agreed to when you signed a sponsorship agreement to sponsor another relative in the past
* defaulted on a court-ordered support order, such as alimony or child support
* receive government financial assistance for reasons other than a disability
* were convicted of an offence of a sexual nature, a violent criminal offence, an offence against a relative that results in bodily harm or an attempt or threat to commit any such offences—depending on circumstances such as the nature of the offence, how long ago it occurred and whether a record suspension (formerly called “pardons” in Canada), was issued (See Sponsorship Bar for Violent Crime below)
* were previously sponsored as a spouse, common-law or conjugal partner and became a permanent resident of Canada less than 5 years ago (See Five-year Sponsorship Bar for persons who were sponsored to come to Canada as a spouse or partner below)
* defaulted on an immigration loan—late or missed payments
* are in prison or
* have declared bankruptcy and have not been released from it yet."
Source: http://www.cic.gc.ca/english/immigrate/sponsor/spouse-apply-who.asp
In the link above you can check the "Sponsorship Bar for Violent Crime".