Your problem is having the US citizenship while living and working in Canada. USA and Eritrea are the only 2 countries in the world that tax their citizens working and living abroad permanently. Most of the time, there are tax treaties that provide that you will not pay additional taxes to the US if you already pay your taxes in Canada. However, it is not always the case. If a Canadian tax exemption is not recognized in the treaty, you may end up having to pay a lot of taxes to the US even if you did not live or work there.
My mother had the dual US-Canada citizenship. She always worked and lived in Canada and always paid her Canadian taxes. A few years ago, she was told that she owed 500K$ to the US IRS due to her US citizenship. She managed to have it reduced significantly and she renounced her US citizenship afterwards, but it is certainly something to have in mind.