Just to add to what Steve said. If you are using a duty holster either it must conform to the specifications for the holster - see page 29 - 35 of the rule book or alternatively be worn on your duty belt with all of the regular attachements and equipment. The latter applies if you are a Police /MilitaryOfficer. In addition we have a Canadian Exemption for military personnel. The Exemption is located on the forum portion of the IDPA Canada website under "Rules Clarifications".
If you are a Police Officer and you choose to use your duty belt/holster/gear then a cover garment is not required.
Take Care
Bob