I agree that young saffrons and adult canaries (at least its yellow version) are very alike. I however thing that with experience, it becomes easy to spot the difference, doesn't it?
In any case, thanks a lot for all these pictures. They are beautiful and well illustrating the point.
Between the juvenile saffron finch and the adult wild canary, I think it is necessary to have a lot of experience observing them closely, from far away I believe it would be very difficult to detect the differences.