Locations that record iris scans are listed here (with hours of operation). No appointment is necessary (or possible) for adding an iris scan to an existing Nexus membership:
https://www.cbsa-asfc.gc.ca/prog/nex...ation-eng.html
Please note that CBSA is retiring iris scans as the "fingerprint" for Nexus in favor of facial recognition (photograph). At some airports, iris scan machines are no longer present:
https://www.cbsa-asfc.gc.ca/prog/nexus/kiosk-eng.html
https://www.cbsa-asfc.gc.ca/prog/nexus/rec-eng.html
Notice: Modernizing NEXUS Air Processing at Canadian Airports
The CBSA is modernizing the way NEXUS members are processed at Canadian airports. The existing NEXUS kiosks that use iris recognition technology are being replaced with new, modernized NEXUS kiosks that use facial verification technology. The new kiosks are now available at Vancouver International Airport, Montréal-Trudeau International Airport, Halifax Stanfield International Airport and Ottawa Macdonald-Cartier International Airport. The new kiosks will be installed at other Canadian airports in the following months.