FlyAAway,
If you decide to ticket this using a 1-World Explorer from Canada you will need to return to the same country (Canada) of origin. However the rules are pretty flexible so you could actually add SEA-MIA-DFW-YVR segments to your ticket at no extra cost and get a free trip to MIA. These segments can be taken at any time up to a year out. It would also solve the 10 day minimum stay requirement if that was a problem.
Also do not forget that CX does not offer First from HKG to DXB, however if you wanted to be a mileage "hog"

you could fly YVR-HKG-LHR-DXB-LHR and get the First Beds the entire way at no added cost.
Have a good time on the flights and make sure to sign up for the Cathay Loyalty bonus.
rrich