If a recipe calls for canned beans and I want to use dried beans, what do I need to do to the dried beans first

The toxin in kidney beans is destroyed by boiling for around ten minutes, which no doubt holds true for any toxin in the water as well. So there should be no problem with using the soaking water to cook the beans, provided you cook them properly.

If Wikipedia is to be trusted (and in this case, their source is the FDA), there is in fact a toxin in some raw beans, such as kidney beans.

The toxic compound phytohaemagglutinin, a lectin, is present in many common bean varieties, but is especially concentrated in red kidney beans. White kidney beans contain about a third as much toxin as the red variety; broad beans (Vicia faba) contain 5 to 10% as much as red kidney beans.3

Phytohaemagglutinin can be deactivated by boiling beans for ten minutes; the ten minutes at boiling point (100 °C (212 °F)) are sufficient to degrade the toxin, but not to cook the beans. For dry beans, the U.S. Food and Drug Administration (FDA) also recommends an initial soak of at least 5 hours in water, which should then be discarded.3

During the pressure-canning process beans undergo (they are fully cooked in the can), the toxin is certainly deactivated. Canned beans are ready to eat, even cold, although they probably taste better hot, and with some flavor from a sauce or accompanying dish.

The danger would be in slow-cooking dry beans of this variety, which have never been previously cooked.