It’s not unusual to see Canadian A320s in Boeing Field.  They provide a lot of sports charters but, until recently, these were usually undertaken by Jetz aircraft.  More recently, it seems that they have transitioned to jets in the Air Canada core colors.  Since Air Canada has been taking delivery of lots of 737 Max aircraft recently, maybe they are cascading some of the older mainline jets to the charter operations.  I don’t really know.  I only know I have shot a few of their aircraft at Boeing Field recently.