I assume you hold a non-visa exempt passport and require a visitor visa to enter Canada. If that's the case and the US deportation is relatively recent (within the last few years) - it's unlikely the visitor visa will be approved since the illegal entry and deportation demonstrate past abuse of immigration rules and priviledges. You will need to provide more information in order for us to provide a more definitive answer - information like: visa exempt or non visa exempt passport, country of origin, when the deportation took place, how long the person was in the US illegally before being deported, what ties they have established to their home country since the deportation.
