If you are required to make personal income tax instalments then the first one for 2017 is due on March 15, 2017. This instalment is based on the amount of income you earned in 2015, so you should already know the amount that you have to pay. The instalment was listed on the letter that you received from your tax preparer with your 2015 tax return.
Your 2016 tax return is due by the end of April 2017 – therefore CRA does not use the 2016 return to figure out the first two instalments for 2017. This is simply because they do not have the information yet. The September 15 and December 15 instalment will be based on 2016 returns.
It may seem a bit unfair that you are being asked for 2017 money before you file your 2016 tax return – but that is the rule.