Please go through section 15 and IMM5612E.It's not just having liquid cash. You MUST show that the money was not borrowed. That's the whole point of a 6 month average balance or bank statement. The only exception is a gift deed.
There are several threads explaining the same thing. Here's one: https://www.canadavisa.com/canada-immigration-discussion-board/threads/fixed-deposit-as-proof-of-funds.394087/
You must be able to use this money to pay the costs of living for your family.....so FD suffices not to be a six month old constraint.