CMHC sets a minimum credit score of 600 for an insured mortgage, so below that threshold the conversation genuinely is about approval. Above it, the remaining effect shows up more in the rate and the lender options available than in a yes or no answer.
A borrower with a strong score but debt ratios near the CMHC guideline ceiling can still land a middling offer, because the lender is weighing the whole file rather than treating the score as the only number that matters.
A mortgage broker can show what a specific score and debt ratio actually translate to in rate terms. Get your hand-reviewed valuation from Joel Dyck.