There are no borders in nature.
There are between 12 and 20 million tonnes being pushed into the ocean every year. That's got to go somewhere. When plastic breaks up in the ocean, whether it's through rubbing on the sand on the beach, UV or salt, it can come back in the air. It doesn't matter where that plastic went in; you can be breathing it in Canada and anywhere else on the planet.
My research is up in the free troposphere as well, which is above the clouds. That's the superhighway for plastic and all chemicals. Plastic can go around the world in two weeks, so as for shipping your plastic away, there's no “away” for plastic. There's no, “I will just send it to Asia, because they can recycle it.” It doesn't get recycled; it's burned. It gets pushed into the river. There's ample proof of that. Read the Interpol reports, please. I recommend everyone that does that.
I'm currently researching plastics up here in the Arctic, but my NGO is tackling plastic waste going into the river in Asia as a start, because the majority of plastics in the oceans come through Asia, because western countries thought Asia was a good place to dump their waste. They didn't have any way to recycle it.