What are the circumstances under which a person will be denied canadian citizenship?

You cannot become a citizen if you:

are on parole or on probation or serving a term of imprisonment in Canada

are serving a sentence outside Canada

are charged with, on trial for, or involved in an appeal for an offence under the Citizenship Act, or an indictable offence in Canada,

are charged with, on trial for, or involved in an appeal for an offence committed outside Canada that is determined to be equivalent to an indictable offence in Canada

are under a removal order (Canadian officials have asked you to leave Canada)

are being investigated for, are charged with, on trial for, involved in an appeal for or have been convicted of a war crime or a crime against humanity

have had a citizenship application refused for misrepresentation in the past five years

have had your Canadian citizenship revoked (taken away) because of fraud in the past ten years

have been convicted of an indictable offence in Canada or an offence under the Citizenship Act in the four years before you apply

have been convicted outside Canada of an offence that is determined to be equivalent to an indictable offence in Canada in the four years before you apply, even if you were pardoned or otherwise granted amnesty for the offence,

have been convicted of terrorism, high treason, treason, or spying offences while you were a permanent resident,

served as a member of an armed force of a country or organized armed group and that country or group engaged in armed conflict with Canada, while you were a permanent resident, or

never met or no longer meet the requirements for a grant or resumption of citizenship.

(https://www.canada.ca/en/immigration-refugees-citizenship/services/canadian-citizenship/become-canadian-citizen/eligibility/situtations-prevent-citizenship.html)