Most simple method is to use single quotes on the right hand side:
if [ "$line" == '#orb_plugins = ["local_log_stream", "iiop_profile", "giop", "iiop"];' ]
This way the string to be matched is interpreted literally.
If you prefer using double quotes, you do not have to escape the brackets ([]), but only the double quotes (""):
if [ "$line" == "#orb_plugins = [\"local_log_stream\", \"iiop_profile\", \"giop\", \"iiop\"];" ]