If you are a US citizen, you are taxed on your worldwide income, so yes, as long as you are a citizen of the United States, you have to be worried about US taxes anywhere and everywhere you make money. The US is one of a handful of countries that tax you on worldwide income. (Please also see my answer under “How does the Foreign Earned Income Exclusion work if I live in Belize” for how some taxpayers can exclude some income from US taxable income.)
Whether or not you pay Canadian and other countries’ taxes are dependent on where you actually reside. Unlike the US, other countries allow you to declare your residency, and if you stay out of your home country for a period of time as defined by your home country, then your residency status would be changed such that you would not owe taxes to your home country based on your worldwide income.