so would you suggest fiancé (if there really is an engagement) or "significant other"? remember there is proof that kids are involved!
Don't say anything about kids or fiance. Say you are going as a tourist or if there is a possibility to be invited by a same sex friend. Even invitation by a sibling, aunt or uncle is better than significant other/fiance/spouse/bf/gf/lover/etc (the latter category is the highest pull factor to Canada.
Now if you get married and now a spouse, of course you cannot mislead ircc because they will find out about it when you apply PR and they can ban you for misrepresentation.
Again, I'm not saying that declaring yourself a fiance is automatic refusal, they still will weigh your home ties against this HUGE pull factor to Canada.
In rare instances if the officer in a very good mood, they can give visa for fiances, fully expecting the couple to apply inland for PR...but thats rare like snowing in Jerusalem.