I never believed the line "it is 1945 and nobody cared". An army survives on discipline and dress regs are a large part of that.
This Private should have belonged to some unit prior to his posting to CFPU and should be wearing the cap badge of that unit. He should also be wearing a formation patch, as do the others in the photo. If he was based at CMHQ I can assure you that MPs and/or Senior Officers would have pointed out to him (or to his CO) his dress transgressions.
Most of the correspondence on the "USA" identifier originated in London in the 1940-41 era and the decision was final. Four years later is not a long time in military memory and, if he was indeed an Amercan enrolled in the Cdn Army, he would have not been permitted to wear this.
Despite the caption - which are often written to satsify the needs of the day - I believe that this individual may have been a US national working as a correspondent for Maple Leaf (as opposed to a War Correspondent working for a newspaper in Canada). If we could see the colour of his tie we would know if he was an officer "equivalent" or not.
Dress regulations would not have covered this and his greatest dress transgression would be his wearing of the CFPU patches (the unit he calls 'home') instead of the "Canada War Correspondent" flashes. This would explain the 'USA' identifier and why no-one challenged him on it.
My tuppence worth.