From the Washington Canadian Embassy web site:
“Members of Inadmissible Classes include those who have been convicted of MINOR OFFENCES (including shoplifting, theft, assault, dangerous driving, unauthorized possession of a firearm, possession of illegal substances, etc.), or of INDICTABLE CRIMINAL OFFENCES (including assault with a deadly weapon, manslaughter, etc.). As well, those who have been convicted of DRIVING WHILE INTOXICATED (DWI) are considered Members of an Inadmissible Class. Driving while under the influence of alcohol is regarded as an extremely serious offence in Canada.
Those who have received TRAFFIC VIOLATIONS (including parking/speeding tickets, etc.) and other minor violations (i.e. littering, etc.) most likely will NOT be prohibited from entering Canada. Similarly, those who have JUVENILE CONVICTIONS (convictions for crimes committed while under age 18) most likely will NOT be prohibited from entering Canada unless they could have been tried as an adult for their offences. “
Read more, here.