The similarity between the methods that Cavour and Bismarck used in their attempts to unify their respective nations can be summed up in their employment of the concepts of realpolitik, war, and diplomatic manipulation.
Both men were strong nationalists and monarchists, but that seems to be where their ideals ended. They did not shy away from lying and cheating to achieve their goals. In their efforts to unite their nations, they focused on "practical" matters, even if many would find their actions immoral. To Cavour and Bismarck, the ends justified the means.
For instance, Cavour knew that he could not achieve his goals without outside help from a strong foreign power. Napoleon III seemed like a good potential ally for him. Cavour secretly negotiated an alliance with the French and then instigated a fight between Sardinia and Austria to get them involved. Following this short war, Sardinia and Lombardy were joined. Later, Cavour organized votes in other Italian lands his army had occupied, against the wishes of Garibaldi, in which Italians voted to join Sardinia.
Bismarck also used deceit to achieve his ends. Like Cavour, he goaded Austria into attacking his country. Austria's defeat resulted in the end of the old German confederation. Bismarck was then able to form a new confederation of northern German states, with Prussia at its head. In order to get the southern German states on board, Bismarck instigated a war with France. The southern German states, therefore, had little choice but to join the new German confederation for their own protection.
As you can see, both Cavour and Bismarck attained their goals by tricking their neighbors into starting wars and making beneficial, if manipulative, diplomatic alliances.