I don't think there is a fixed duration for the bank account statements to be submitted in support of a Temporary resident/ Visitor visa application to Canada.
You can check this link to understand what the officer is required to review
https://www.canada.ca/en/immigration-refugees-citizenship/corporate/publications-manuals/operational-bulletins-manuals/temporary-residents/visitors/proof-funds-financial-support.html
The Visa Officer (VO) is likely to consider the overall profile before coming to any decision. As an example, say my salary is US$ 3,000 a month and I have a large bank balance of US$ 80,000 or so....then the VO is likely to be concerned if I 'borrowed' these funds to paint a better picture or have been consistently depositing regular amounts to create such a balance. Say I was unemployed for 8 months in the last year, then such concerns become even more critical.
Perhaps in this case, the duration of the bank statements assume a higher significance to prove a legitimate source for such funds along my tax returns filed in the last couple of years. On the other hand, if my monthly salary has consistently been US$ 10,000 a month then the balance is a lot more plausible and perhaps a lesser duration of statements is acceptable.
The duration of your visit, a good level of income in your home country and funds available to support your travel costs to and from Canada, as well as all activities for the duration of your trip in Canada are all equally important.
Even if you do have say a large deposit just before you obtained the statement, then its ok to clarify it in your 'Letter of Explanation'. Do not leave anything to doubt.
If your previous application for a visitor visa was rejected, you need to focus on the reasons provided for such rejection. If you are unsure and have at least a month until you need to submit your current application, then it might be worthwhile to apply for GCMS notes to understand the VOs specific concerns. This way, you can address each one of them and achieve a favourable outcome.
