"What is the difference. Are they uncannonical? If so how are they uncannonical?"
FYI:The following remarks are very broad.
The style of Western icons is "naturalistic"; that is, they more nearly attempt to resemble visual reality. The rendering of the forms, the composition and perspective, the treatment of light, the features of the subjects--all are realistic. Also, there is much more latitude in subject matter--imaginary scenes are permitted--and much more emphasis is allowed on the idiosyncracies of the individual artist and the contemporary painting style. For instance, 19th century Russian icons were affected by the prevailing Romanticism and sentimentality of the age. Consequently, to my mind, they're very weak and have a tendency to look dated.
In comparison, Eastern icons are technically primitive and inartful: the drawing is naive or expressionistic, the composition unsophisticated, the perspective irrational, the proportions expressionistic. They are purposely designed not to look realistic, but to transcend space and time. Also, the subject matter is highly circumscribed: it's limited to scenes represented exactly as they are described in the Bible, with no major changes allowed because, originally, icons were used to teach the Gospel to the illiterate. The symbology and rubrics of the icon are very precise: the colors, the figures, the positions of the eyes, the hands, the heads, etc.. In addition, the artist is--or should be--anonymous. Theoretically, the iconographer is more devout than artistic and is channeling the Holy Spirit. The office of iconographer is considered a special ministry and is one usually occupied by monastics. Obviously, a talent as great as someone like Rublev is going to shine through; he has a very identifiable style and doesn't have to sign his icons, but the ability to paint a spirit-filled icon is considered a gift of God and primarily a spiritual, not an artistic, charism.
The fundamental idea in Western icons is this world; the fundamental idea in Eastern icons is the next. Not to say that much Western religious art isn't supremely beautiful--of course it is. But it's more decorative and art pour l'art. Icons have a very specific religious function which has nothing whatever to do with conventional ideas of earthly beauty.
From the strict perspective of Orthodox iconography, western-style icons are considered uncanonical because they do not transport us to a contemplation of the next world, the world of God and the Uncreated Light; neither do they reflect the transcendent quality of the saints. Rather, they keep us bound here, to this world and all its temporal follies. At their worst, they do not always express correct theology.
I'm grateful for the resurgent interest in traditional iconography, and I'm waiting for some spiritually gifted iconographers to come along. Much of what passses for iconography right now is, to put it baldly, kitsch.