You are registered in Canada, there is no need for a new account. You simply have to close the US Store and open a Canadian Store.
One issue you will have with that is that you will not be able to use the same Store name until it has been unused for 30 days.
The other issue you will have, if your payouts are currently in US Dollars then you can't change that to CAD, it would require a new account. Unlike in the PayPal days when payouts currency could be changed once a year with MP that is not possible. Moving to a CA Store will be cheaper but it won't change the payout currency.

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
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