So to clarify, the max unassisted speed on any production ebike is 20 mph. The class 3 bikes will have an assisted max speed of 28 mph, and some will have an "off-road" mode that will allow assistance above 28mph.
However, you need to understand maintaining 28mph requires a LOT of energy from the battery. You are likely to use ~30 watts/ mile at that speed. Thus your 12 mile commute will use ~ 360 watt/hours each direction. Thus you will need a battery with a minimum capacity of > 720 W/h, and even then you would be using nearly 100% of your battery. That is not good for battery longevity, and you will find your range decrease over time fairly rapidly.
Now there are plenty of ebikes that are class 3. But only a few have battery options > 700 W/h. Your price range will determine what is available to you. On the low end price wise, Juiced Crosscurrent S has a 48V, 19.2 Ah battery option (922 Wh) for $1999, (they have a bigger 52V/ 21Ah option for $2999). The problem here is primary high demand, the bikes are currently backordered until May. On the high price end of the spectrum, Reise and Muller Supercharger has a dual battery option for 1000 Wh that runs ~$7000.
If you provide more info on your price range, riding preferences, need to maintain highest posible speed, etc. I'm sure others will provide feedback as well.