1/ surprised: ~ at/by sb/sth), ~ that…; ~ (to see, to hear, etc); see OALD.
This means that "surprised seeing" should not be used; however, this usage has come into being in the present century, as shows Google Books. There is no difference, then.
"Surprised seeing" should not be confused with "surprised, seeing"; in this latter arrangement there is no direct link between the object and "seeing" and the adjective, whereas when the comma is not used what causes the surprise is embodied in the object of "seeing".
2/ nice ~ to do sth; ~ doing sth; ~ that …; see OALD.
Therefore there is no difference.
3/ The construction "impossible seeing" feels even stranger than the construction in "1/" (it is not recorded in OALD); this is corroborated by the following findings.
The situation for "impossible" tends slightly to be that for "surprised", but only slightly. If you examine Google Books you will find numerous false positives (of the sort "impossible. Seeing…") and the construction "impossible, seeing", another false positive, but very few cases of "impossible seeing". It follows that, given the general trend we are bound to accept the two construction and consider they have the same meaning. However, some people might want to reject "impossible seeing" while considering "surprised seeing" acceptable.