It's better to file your tax return on time unless you are 110% sure you don't owe any amount to the CRA.
Otherwise, you will be penalized and will be asked to pay interests as well.
If, you owe money to CRA, you have to file your tax return on time with at least the following two things.
1. fill out all the original data with all the proof/forms;
2. write a cheque with an estimated amount (the closer the better, if you are not sure, then make sure it covers what you guess).
The CRA will calculate your return according the data you provided, you won't get penalty for unable to do the very complicated math as long as you finished those two things on time.