Yes, it will be 10 for the whole thing. You pay the 10 when you upgrade CUN-YYZ at T-21, then there's no additional debit at T-14 for YYZ-YVR.
A year ago I had SFO-YYZ-AMS // LYS-YUL-YYZ-SFO, booked in NNNBN. The upgrade windows were 14, 7, 7, time-of-booking, 14. So things were upgraded in a very odd order, but it all priced out exactly as expected in the end.