I have frequent flyer status with Turkish Airlines which gives me Star Alliance Gold status.
Using Kayak to search for flights, I want to know, prior to purchasing a ticket, that I am able to upgrade an economy class ticket to business class using miles (i.e. a non restricted fare).
Is this something that can be inferred? Alternatively, are there other tools I should be using to get this information?
Given that you are looking to upgrade a flight on an airline other than the one you have status with, what you are referring to is a Star Alliance Upgrade.
These upgrades are generally only available on very expensive fares - on most airlines (including United) they are only available on "B" and "Y" fares, which are the two highest level of Economy fares.
In the screenshot you've shown, the fare class is the first letter of the fare code shown - "W" and "L". "W" is a mid-way economy fare class, and "L" is a very low fare class - both are a very long way from Y/B.
An equivalent B-class fare will likely be at least 2-3 times the price shown, probably more. Even then, upgrades are limited and there is no guarantee that you will get one - especially on an airline like United who offers multiple ways for their own frequent flyer members to upgrade, so you will be fighting with those people for the few upgrade seats that may be available.
Fare class is one, but far from the only, determinant of whether a ticket is upgradeable.
You must also factor in
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.
