This is the message I got from IRCC:
For you, the principal applicant,
if not yet submitted:
Offer of Employment:
If you have an offer of employment in Canada, you must submit an updated copy of the employment offer from your employer in Canada dated this year.
Employment Reference Letter:
A letter for each declared period of employment.
Education Credentials:
All documentation (diplomas and transcripts) to support your declared post-secondary education or vocational training.
Language Abilities:
Any documentation you would like to submit as evidence of your abilities in either of Canada’s official languages, English or French. You are strongly encouraged to submit the results of an IELTS/CELPIP exam or Test d’évaluation de français (TEF).
Proof of Funds:
Any evidence of funds that will assist you in establishing in Canada.
Any other documentation you would like to submit as evidence of your ability to become economically established in Canada.