How large are chances for a person which get highest honor diploma in
the theoretical physic (in Ukraine) and is finishing PhD in
theoretical chemistry (in Germany) to get a postdoctoral position on
the Department of Computer Science of the University of Toronto?

You may want to check the U of T computer science homepage:
http://www.cs.toronto.edu/DCS/index.html

Not knowing which universities you attended in Ukraine and Germany, it
is difficult to say whether or not any previous credits would
transfer.  However, as long as you can pay tuition, I wouldn't forsee
a problem with applying.

It does seem to me, however, that your fields of theoretical physics
and theoretical chemistry may not be the most applicable to a
westernized course of study in Computer Science.  Instead, you may
consider applying for an assistant or adjunct position with the
physics department at University of Toronto.  However, if you're
dead-set on U of T, you can try one of the following phone numbers:
Departmental Office:  416.978.6025
Graduate Program:  416.978.8762  (Assoc. Chair Graduate Coordinator, Richard Zemel)
Office of the Chair:  416.978.2980

You will probably have to apply to the University of Toronto through
the general applicant pool.  Get "Prospective Student" information at
http://www.toronto.edu/Prospective_Students.htm

I can't speak specifically for U of T. At the University where I am it
is not uncommon for computer science post-docs to not have a computer
science degree. Istead they have a degree in biology, chemistry or
physics and in these fields have heavily used computers for their
research. There's no hard rules. It's up to the PI to decide what is
appropriate.