Not to mention unless it has some weird title that lets it fire both cannons, theres literally no point in double cannon slot.
You can only ever use one, and the other would just add points for little to no gain.
Now what would be interesting is if you could fire one cannon and apply the effect of the other as well. Fire a Mangler Cannon that also applies an ion token ftw lol
Problem is, that's going to get wordy if you have a mix of weapons with varying ranges (like a heavy laser cannon and autoblasters, for example).