Well... first to test a command you don't need the square brackets nor the back ticks, e.g.
here the exit status of the command is used as true (0 = success) or false (1 = failure). Second, I have some doubt about the ssh command you used. In openssh the -C option has a totally different meaning from "execute a command to the remote machine". What version of ssh are you using? Is this a linux box?
Here is what you can do if using openssh, to test the existence of a regular file on the remote machine:
if ssh user@host "test -f /path/to/remote/file"
echo file exists
echo file not found
Hope this helps.