In order to answer the questions brought up in this thread, one has to maintain a consistent point of view. Initially, wcflex stated that he is a dual national (ROC - Canada) and has an ROC ID card. Based on that status, which is quite a bit different from "overseas Chinese", and certainly different from "average foreigners", of course he has full work rights in the ROC.
Article 7 of the Income Tax Law does not differentiate between local citizens and foreigners in terms of the amount of withholding taxes which should be taken out of salary payment for services rendered in the ROC. Hence, for those physically present in the ROC less than 183 days in the year, withholding should be made at the 20% rate.
If your employer is not doing this, he is not conforming to the law. Unfortunately, such non-conformance to the law is commonly seen here in Taiwan.