Yes, Canadian residents need a visa to work in Ireland. Canadians who want to work in Ireland need a visa or work permit, even though they do not need a tourist visa for visits of up to 90 days. The visa-free entry does not allow work.
To work in Ireland, Canadians have to apply for a work permit, like the Critical Skills Employment Permit or the General Employment Permit. The permit needed depends on the job and salary. Either the employer or the applicant needs to apply through Ireland’s Department of Enterprise, Trade and Employment (DETE) before starting the job.
You cannot enter Ireland to work without getting a permit first.