This eight or ten digit number looks like this: 0000-0000 or 00-0000-0000.
Look for this number on:
letters we sent you
your immigration document such as a PR card, study or work permit
If you do not have any of these documents but want to fill out an application form, you can leave the field for UCI (Client ID) blank.
If you have not dealt with us since 1973, you will not have a UCI or a Client ID.