<HTML>There is treaty between US and Canada. First you will be charged for US tax when you get pay. If you do not abandon residence in Canada, you must file tax return in both US and Canada, but the US tax can be counted in Canada tax, that means you won't be charged twice. By the way, there is also US-China treaty. If you can find some loop hole from these two treaties, that would be great, though the method is very compicated.
good luck.</HTML>