ITR is just one of the recommended POF. However you can always get authenticated bank statements as additional proof apart from GIC. Just ensure you don't have big amount credited within short period of time.
As per IRCC guidelines below are list of acceptable proof for funds. It does not explicitly say fixed deposit as they are usually a fixed term hold and IRCC is mostly interested in liquid funds that you can use in Canada during your stay.
proof of a Canadian bank account in your name, if you've transferred money to Canada
Guaranteed Investment Certificate (GIC) from a participating Canadian financial institution
proof of a student or education loan from a bank
your bank statements for the past 4 months
a bank draft that can be converted to Canadian dollars
proof you paid tuition and housing fees
a letter from the person or school giving you money or
proof of funding paid from within Canada, if you have a scholarship or are in a Canadian-funded educational program