There are not "thousands of incoming oil tankers" on the east coast every year.  

Canada currently imports about 700,000 bbl/day, and more than half of that is from the US, much of which is shipped by pipeline or train.  But even if all of our imported oil was transported by tanker -- which it isn't -- that would require maybe 1 medium-sized tanker per day, or 2 smaller ones, but certainly less than one thousand per year, never mind the "thousands" you claim.