This question has bothered me for some time. Both Canada and Russia have vast regions with a temperate climate. Both have been subjected to extensive immigration policies yet both are (from what I hear) net importers instead of exporters of food. Every once in a while it is said that the ground would be unsuitable for cultivation but this has never been expanded upon which increases my curiosity.
Just because there's dirt there doesn't mean you can farm. And even if you can farm it, that doesn't mean you won't quickly deplete the soil.
I did a fair bit of digging (ha!) into Russia's agricultural system a few years ago. The short version of why Russia didn't try to farm Siberia is that the black earth region that makes up the best Russian farmland isn't "maxed out," so to speak. Arable land has dropped to 7.4% of total land area, down from 8.1% in '92. Total agricultural land is a little less than double that, coming in at 13.2% (this is the total percentage of land worked; about half the space is devoted to pastures and the like).
Russia is odd in that it seems to be a net exporter of food (in terms of calories), but a net importer in terms of value. About a fifth of Russia's farmland is used to produce wheat, which is the largest share (36%) of Russia's food exports. And Russia imports nearly as much value in alcohol as it generates from wheat. Russia also had to rein in export duties on goods like soybeans as part of her accession to the WTO. This definitely impacted the trade balance.
Finally, WTO membership restricted how much money Russia could invest in agricultural products (capped at $4.4 billion in 2018), which, together with relatively low export prices, further discourages Russia from spending money to expand farming.
That hasn't stopped other initiatives, though. A British property developer recently bought 35,000 acres at $100 per and the new start-up turned a profit last year. Considering the enormous amounts of land available, this could turn into an agricultural boom if other companies try to emulate the profits (and if sanctions don't prevent investment).
With regards to Siberia in particular, the Far East district just started offering a free hectare of land to anyone who moves and works it (families can apply for one hectare per person). That's only for Russian nationals, of course, but it shows the kinds of unique ways Russia is trying to put her land to use. Plus they want migrants. There's only a few million in that district.
Both Canada and Russia are large agricultural producers, although they lack most of the absurd fertility of their immediate neighbors in the US and Ukraine. However, the agriculture in both Canada and Russia is largely confined to the west.
For Canada, grains and animal products come out of the central Plains (Alberta, Saskatchewan, and Manitoba) while the west coast of Southern BC has much the same agricultural production as the PNW. Outside these areas, climatic and geological factors make most agriculture very difficult.
The modern city of Edmonton is right on the very northern limit of where you can grow grains commercially due to the short growing season and cold temperatures. Towns farther North must often use greenhouses to artificially extend the growing season. To the east, you begin to run into the rocky, thin soils left behind by heavy glaciation during the last ice age.
In parts of central and southern Quebec, there does exist a band of deep clay soils that would be ideal for agriculture. However, the region itself has a growing season of only two or three months and homestead programs by the government revealed that no one was willing to tolerate the massive swarms of flies that emerge every summer.