Yes, I did the same. Along-with that, I wrote a letter of explanation stating that the T4 is currently not available and I will file the return once it's available. BUT you should have filled 3 tax returns prior to this. If not, I would suggest you wait and file 2020 before applying.
Yes, you don't. Here the text from Q10 on the link I have posted above:
You don’t need to provide a police certificate if
- you were in your country of origin immediately prior to becoming a permanent resident and landing in Canada, and
- this time falls within the past 4 years