I didn't have this situation but i can advise a little about what to write.
Basically you need to plan every thing outright and put in numbers. How much do you earn, what will be the child's needs. If he / she cannot go to regular school for now, what type of school would he go to? Research that and get info from schools websites / reaching out to them by phone. Would that cost any thing additional? What would you be able to pay out of this? Any details on therapies etc. that would be needed.
Also some specialist recommendation on how severe / mild the child's state is and how much therapy support he / she would need to function in every day life.
Parents income, status / financials etc. would help.
I have a vague (though unconfirmed recollection) that CIC weighs all of this against a material number. If they feel the annual cost of health care (specific to ASD only) for the child would be more than 6k CAD, then it is likely to be refused. If it falls below and a formal plan seems viable, they might accept.
That being said, i don't know of anyone with above scenario who went through the entire process and was successful. But i believe that is mainly because CIC notoriously delays such cases and people loose track of getting back to forums in that situation.
All the very best.