In short, canon content:
Precursors campaign
Enslavers I campaign
Insurrection*
Retribution*
Enslavers II campaign
Deception map**
Mercenaries II map**,***
Resurrection IV map**,***,****
* Blizzard is not sure now if they want to consider these campaigns as canon, but when they were published, they were fully authorized campaigns AND the companies that produced them worked closely with Blizzard
**these 3 missions are part of the same storyline and must be played in the order presented here. They are not voiced.
***these are multiplayer maps, but remember, they are canon
****this mission only appeared in Starcraft 64, however, there is a PC port
I’m pretty sure Mercenaries I, and consequently, Revolutions, are canon, but they are so inconsequential to the main lore that I wouldn’t give them much of a thought.
Edit: Ascension of Duran and Interbellum campaigns are fan made. They are neither made by Blizzard, like Enslavers and Precursors nor endorsed by Blizzard, like Insurrection and Retribution. Note how I’m not saying if they are bad or good, just that they aren’t canon.