Yes, a conviction of a crime inside or outside of Canada may make you criminally inadmissible to Canada. There are several factors that determine whether or not such a conviction will prevent you from getting admission to Canada, including the age at which you were convicted, the specific offence, and the time that has passed since that conviction.
If you have an arrest, conviction of which would warrant inadmissibility, and the outcome of the judicial process is not completed, you could potentially be barred from entry until the case is decided.
The severity of the offence in the country in which it occurs is not necessarily the determining factor in determining inadmissibility. Instead, the severity of the crime under Canada's legal system is the determining factor.
For someone arrested or convicted outside of Canada, one indictable offence (generally, one that is eligible to be tried before a jury) or more than one summary conviction (generally, a minor offence) would generally be considered grounds for criminal inadmissibility. An individual who commits an offence in the course of entering Canada (for example presenting false documents) may also be sconsidered criminally inadmissible.
Canada also has mixed or hybrid offences. This means that the same offence is potentially addressed by summary conviction or indictment, the provision for which both fall under the same legal statute. If convicted abroad of an offence that is considered mixed in Canada, then it is automatically treated as an indictable offence for the purpose of evaluating inadmissibility for immigration purposes.
A diminished or suspended sentence is a conviction and may still be grounds for inadmissibility.
A Pardon or expunged record which has been granted outside of Canada does not remove the offence for the purpose of immigration matters. The offence may still be grounds for inadmissibility.
In some foreign jurisdictions, such a pardon, an expungement, or even the passage of time may mean that you are not required to disclose the existence of that conviction under some circumstances, for example to an actual or prospective employer. This does not apply to Canadian immigration processes; the existence of the offence should still be disclosed to prevent the appearance of carrying out an offence (i.e., the impression of lying to an official).
If you were acquitted in court or the case dismissed, then the offence leading to that hearing should not be considered grounds for inadmissibility. However, being able to demonstrate such acquittal or dismissal could be valuable when seeking temporary admission or a work permit.
You must consider the Canadian equivalent of the foreign offence at the time at which the foreign arrest or conviction occurred. If that equivalent is of an indictable offence or more than one summary conviction in Canada, then you may be considered criminally inadmissible.
You may proceed with an application or request for a Temporary Resident Permit (TRP) or an application for Criminal Rehabilitation. A TRP may be sought at any time, and constitutes the documented admission of an individual who is considered inadmissible. A TRP is granted on a single occasion with a fixed validity and only permits admission for that duration. A TRP may be sought in the course of an application for temporary admission to Canada, and may be processed at a port of entry or at a Canadian visa office; if requested at a port of entry, the official may demand that an application be submitted to a visa office.
Once five years has passed since the completion of the sentence resulting from the offence, you may also apply for Criminal Rehabilitation. If this is approved, the applicant becomes admissible to Canada again. So long as there are no further arrests or convictions, this applies permanently.
If an individual has committed only one crime, that crime is not severe (i.e., the Canadian equivalent carrying a maximum prison sentence of less than 10 years), and sufficient time has passed since the completion of the sentence, a person may be considered Deemed Rehabilitated, and may become eligible to obtain a temporary work permit or temporary admission to Canada.