I am not in position to provide factual details, but in my opinion, they won't have access to know all the bank accounts unless the accounts are in Canada. For other countries, they would have to rely on external agencies, and it is unlikely they will engage them specifically for proof of fund, though scrutinized security checks may unveil the financial holdings of an individual.
Also, case officer may ask for source for any credit transaction that he/she may think that may not be your money. It's their discretion. They won't know that in past you have landed the amount to your brother. So better to proactively explain the source and as evidence you can include the debit transaction that happened in past when you have money to brother. That saves time in my opinion.