No, and no.
Current production costs of biochar are in the hundreds of dollars per tonne. (It shouldn't be that expensive.) By comparison the mining costs for coal at my neighbor, the coal mine, run about 90 cents (canadian) per ton. It will be a while.
General paper about biochar with nominal $200/ton wholesale price from a unit that processes 2000 tons per year.
If you are going to burn it, there is little point in converting to biochar. Just burn the starting material. I read one study that in Tennessee it would be possible to raise enough hardwood on the area they were strip mining to power the generators indefinitely. But not as cheaply, but it's much newer tech.
So for sugar cane, it is quite reasonable to extract the juice from the cane, spread the crushed cane out to dry as much as reasonable for your climate, then use that cane for process heat to dry the sap, or to generate power. The most efficient use would probably be to generate power and use the waste heat from power generation to dry the sap. Some of these options would require long term storage of either the raw sap, or the cane. This might make the process uneconomical.
For corn it would be reasonable to harvest, let the stalks dry in the field, then bale them until ready to be burned. The problem: A 1 GW power plant takes a LOT of agricultural waste to fuel. Lots of short haul transport. Even with coal with it's higher density is expensive enough to haul, that where possible they put the power plant next to the mine wherever possible.
Corn is a high nutrient crop. Some of those nutrients stay in the leaves. Ecologically expensive biomass. Switchgrass is one that is promoted as a biofuel crop. In fall the plant salvages most of the minerals back out of the grass. Little there but cellulose and lignan.
The big win on biochar is to plough it back into the ground. The evidence is still unclear as to all of it's advantages, but first looks:
It's a sponge for water. In climates where late rain means no crop this may make a difference.
It's a sponge of nutrients. In climates with heavy rainfall, this can reduce nutrient leaching from the soil.
It is stable in the soil. Where compost turns back into fungi food in months to years, charcoal seems to be stable for centuries.
In principle it should be possible to produce biochar as a byproduct of agricultural waste power generation. (Make the char, use the syngas as the process heat for making the char, and for heating livestock barns. Use surplus syngas to generate power.) This minimises the hauling problem, but means you are stuck with smaller less efficient power plants.
In practice, I've not seen units for sale that were automatic enough for practical use.
There's some indication that soot in dust may not be good for you. Also that with sufficient charcoal in the soil, the very soil can burn. (Even in fire succession forests such as our lodgepole pine, seem to be on mineral soils. Every few fires you get one hot enough to burn the soil.)