There's no format to the letter. Your spouse should say he (with name, id number, passport number etc), husband to you (name, id number, pp number etc) gives you permission to use the funds.
Something like:
This is to confirm that I, XXXXXXXXX am the husband of XXXXXXXXX. We are legally married (see marriage certificate attached to application). I have provided all the necessary documents to show available proof of funds from my Accounts that are in my name, to support our Canadian Permanent Residency application, my spouse being the Primary Applicant.
With this letter, I hereby expressly give my spouse XXXX (ID NUM: XXXX) full access to funds held in the accounts provided, to be used as they
see fit, including for the above-mentioned purpose, and are free of any obligations.
I hope you find the above in order. Thank you for your kind consideration.
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I don't think there is any need to notarise such a letter.