The down payment is dependent on the type of lender you need, which in turn is related to your credit score.
With A side lender the down payment can be as low as 5%. ( assuming the stress test is passed). On the B side lending,
the down payment needs to be a minimum of 20%. Down payment unfortunately will not have an effect on rate. In current market
conditions the rate could be lower on the A side if the mortgage is high ration and insured against default.