Yes, I want to say that until and unless final divorce certificate will not come in my hands, my family composition will not changed. I will be written married till then also.
Please confirm
No, again not an expert - but I believe if you land you MUST say your family composition has changed. The lack of a final legal disposition of your divorce/separation doesn't mean it's not true.
Also: apart from your spouse not being able to immigrate, for you to tell the truth (that you're separated, family composition has changed) is not to your advantage nor potential improper advantage to a third party (your ex-spouse). That makes it far less likely that IRCC or anyone else would think you misrepresented (to gain an advantage).
Beyond this if you have questions you may need to consult a lawyer - there are legal system differences that I'm not qualified to comment on. But generally in Canada the substance (actual change in family) would dominate over the form (receipt of final divorce decree, for example).