Fare class is one, but far from the only, determinant of whether a ticket is upgradeable.
You must also factor in
- the type of upgrade instrument you want to use
- your frequent flyer elite status
- whether one or more segments is a codeshare
- upgrade restrictions imposed on certain routes, aircraft, or travel dates
- restrictions written into the individual fare rules
Of course, the aircraft must have a cabin for you to upgrade to. My suspicion is that YOW-BOS is an Air Canada Jazz flight, which in my personal opinion isn't worth upgrading, but that's up to you of course.
Under Turkish Airlines' Star Alliance Upgrade scheme, you cannot upgrade either an Air Canada or a United flight on a W or L fare. On any participating airline, these are restricted to very high fares, typically Y or B for Economy to Business.
If you have a United GPU at your disposal, which you received as a gift or a customer service gesture, you can upgrade on some routes, but not the IAD-DXB leg which is the only one where it would be worth it. The chart indicates that for United-operated flights to the Middle East, Global Premier Upgrades are not available on flights booked in fare classes Z, P, S, T, K, L, G or N.