From what I understand, global warming will make growing food a lot harder in areas like the American Midwest because temperatures will become too high for most crops. At the same time, Arctic (and Antarctic) regions will heat up and permafrost will melt. Would areas like Alaska, Siberia, and northern Canada then become suitable for large-scale agriculture? And if so, would this be enough to make up for the lost production in warmer areas? Or are there other factors in those areas that would make farming impractical?
Much of the unfarmed area is the Canadian Shield (shades of red below):
The current surface expression of the Shield is one of very thin soil lying on top of the bedrock, with many bare outcrops. This arrangement was caused by severe glaciation during the ice age, which covered the Shield and scraped the rock clean. The lowlands of the Canadian Shield have a very dense soil that is not suitable for forestation; it also contains many marshes and bogs (muskegs). The rest of the region has coarse soil that does not retain moisture well and is frozen with permafrost throughout the year.
I think the "coarse soil" is Glacial Till.
CLIMATE CHANGE ADAPTATION AND CANADA’S CROPS AND FOOD SUPPLY (2013) (122 pages) discusses warming, precipitation, soils and other factors.
There is definitely potential for a northern expansion of agriculture as a result of changes in heat and moisture in [the western prairies], although most of these lands will remain only marginally suitable for farming because of poor soil conditions.
It may be beneficial to look at what we know about agriculture during the Medieval Warm Period to start to get an answer to this question. During this time period, c950-c1250, there was an agricultural revolution in Europe and there is some evidence of barley being produced in Greenland by the Vikings.
Granted there may still be some debate about how warm the Medieval Warm Period was, especially in comparison to what many are expecting will happen in the future, but it does seem like there is a good deal of evidence that during the Medieval Period there was a good deal more agriculture occuring at higher latitudes. This doesn't necessarily answer whether or not the arctic areas will be suitable for large scale agriculture in the future, but if history is a guide, addition northern lattitudes with suitable soils will become more productive.