@tali-aviram,
The code you posted worked for me. I had to change a couple of line
breaks, but I think that's because of the way google groups formatted
it (a gist works better of this sort of post.)
The behaviors like this also invoke the opposite behavior, so
show('province_field').when('country').is('Canada');
Also, in effect, invokes:
hide('province_field').when('country').is_not('Canada');
The line breaks that messed me up initially didn't cause any errors in
Firefox, but did show up on the Safari web inspector console, so try
that.
Hope that helps.
Nathan