Although it is usually fairly easy for a Canadian to come to the US and work, but much harder for an American to work in Canada, there are some substantial legal obstacles to what you have in mind.
First, only American citizens (not green card holders) can be USCG licensed as merchant marine officers, including as ship pilots. It would take you five years plus to become a US citizen. It would probably take you three years of full time college in the US to qualify to sit for a license. Then you would need considerable seagoing experience to be a viable canadate for membership in a pilot’s association.
Although it would be time consuming, it would probably be much more practical for you to become a pilot in Canada.
if you have some capital to invest, there are many marine related companies of various sizes in the US and Canada that could benefit from your capital and talents. Marinas, yacht brokers, yacht charters, marine surveyors, marine construction and dredging, boat repair, tugboats, passenger boats, in either or both the US and Canada, are all things that you might want to consider. Especially if you can qualify for a US investor visa.