TPE-ONT flights by CI started with the first flights on Sunday, March 25, 2018. Link: Ontario welcomes China Airlines Taiwan service Markets Insider

This snippet form the article is very surprising to me:
"China Airlines, which increased flight frequency from four to seven days a week in response to strong customer interest, is marketing Ontario as Southern California's new gateway to Asia, a reflection of how far the airport has come since its transfer to local control in November 2016."

And to those who claim there is little freight infrastructure at ONT, FedEx, UPS and Prime Air (Amazon) would beg to differ.