If you only want to use all commanders in non-competitive play (vs. AI or friends), certain mods unlock them within specific match types.
Players often use specific Steam Workshop maps to speed up the Supply grind: company of heroes 2 how to unlock all commanders
The Steam Store often runs sales where Commander DLCs are very cheap (under $1–$2). If there is a specific historical commander you want immediately, buying the DLC is the fastest route. If you only want to use all commanders
Do you need to grind for 1,000 hours? Pay real money? Get lucky with loot drops? company of heroes 2 how to unlock all commanders
Unfortunately, there are commanders that are now completely impossible to unlock if you didn't play between 2013 and 2016. Do not fall for scams selling "game keys" for these.