From one cable, a briefing for President Bush before a trip to Canada in November 2004:

A potential irritant on the Canadian side that may be raised has to do with sharing of intelligence regarding Iraq operations. The government is aware that we are creating a separate US-UK-Australia channel for sharing sensitive intelligence, including information that trationally has been U.S. eyes only. The GOC has expressed concern at multiple levels that their exclusion from a traditional “four-eyes” construct is “punishment” for Canada,s non-participation in Iraq and they fear that the Iraq-related channel may evolve into a more permanent “three-eyes” only structure.