No it won't
Those little pockets are alluvial valleys and and there are very few.
Taiga soil, what little there is is NOT arable - it was all pushed south by glaciation to form the great plains and the steppes in Russia.
While the temperature may be fine for crops - there will be no suitable soil. Pockets do not make food baskets for the world and it's flat out wrong.
Despite the huge expanse of land in Canada’s north, possible climate warming will not result in large increases in potentially arable land. Much of the land is within the Boreal Shield Ecozone has shallow, rocky, often sandy, acidic and generally infertile soils. There are lands with potential such as the soils of the ‘northern clay belt’9. Silty to clayey glaciolacustrine deposits occur in patches within the Canadian Shield from Saskatchewan to Quebec, with a total area of about 10 million hectares, perhaps one-third of that in blocks suitable for agricultural development.
so at most 3 million hectares of our total 52 million.
http://www.prairiesoilsandcrops.ca/arti ... icle_1.pdf
and the same will apply to Russia those the big river valleys that flow north will help a bit.
It will not come even close to offsetting the desertification in marginal water lands all over the globe and the loss of incredibly fertile lands south of the Himalayas - some of which is already subject to salt water incursion into the water table.
http://blogs.nature.com/climatefeedback ... limat.html