Using only current data, with which among the following countries, Russia, Bulgaria, and Estonia, would Canada do best in terms of business relationships?

Deciding which of the following countries--Russia, Bulgaria, and Estonia--would best represent business opportunities for Canada is a multifaceted question, with several variables to be considered. The first such variable involves the integrity of the legal and commercial systems established in each of these three candidates. When considering business relationships, especially when dealing with a country like Canada where the rule of law is strong and the level of systemic corruption is among the lowest in the world, a decision with respect to other potential business partners should include careful consideration of the legal systems in each of those countries. In short, the lower the level of systemic corruption, the safer the country is to do business with.
The main non-governmental organization involved in tracking corruption in every country of the world is Transparency International. Transparency International's reports and country ranks are widely consulted both in and out of government because of the credibility of this particular organization's data and processes. If one consults Transparency International's most recently published data for 2016 (a link to their 2016 report is provided below), it is clear that, of the three countries specified, Russia is easily the most corrupt and, consequently, the least friendly to foreign corporations hoping to invest in Russia's economy. Transparency International, in fact, ranks Russia as the 131st most corrupt country in the world out of a ranked total of 176. Estonia is the least corrupt among the three countries, ranking 22nd out of 176, with Bulgaria in the middle between these other two nations.
Another factor in determining which among the three countries should be the target of Canadian investment or business opportunities is the strength of the underlying relationships between Canada and each of the three countries. Canada is a member of the North Atlantic Treaty Organization (NATO), the multinational alliance of democratic countries that pledge to come to each other's defense in the event of a military attack from a non-NATO country. Bulgaria and Estonia are also members of NATO, having ascended to alliance membership following the end of the Cold War. Russia is not only not a member of NATO; it is, in fact, the acknowledged greatest single threat to the security of NATO members. Relations between NATO and Russia today are the most tense they've been since the height of the Cold War, a factor that Canada cannot possibly ignore, especially given the sanctions imposed on Russia by the Western countries in response to Russia's invasion of Ukraine and annexation of Crimea. Additionally, Russia increasingly threatens Estonia, as well as the other Baltic countries Latvia and Lithuania, with threatening military exercises and activities intended to intimidate these tiny, relatively newly independent nations.
The overall business climates in each of the three countries could be considered a wash, but with Estonia emerging the victor for its Western orientation and relations with the countries of Scandinavia. Russia has a large economy and a large population (143 million people versus 7.26 million for Bulgaria, and 1.325 million for Estonia). Those are factors that cannot be ignored when considering potential foreign markets and trade partners. 143 million people constitutes a much larger market for Canadian exports than do the very small populations of Bulgaria and Estonia. In fact, the latter two countries' economies are so small that they can't possibly compete with Russia as a potential major trade partner. What they do offer, however, that Russia cannot is their membership in the European Union, which binds them to certain budgetary practices (exempting for the moment the failure of so many EU members to meet mandatory budgetary targets, and the ongoing dissension within the EU regarding immigration policies). More importantly, the EU is closely tied culturally, economically and politically to the United States and Canada, making a relationship more likely to succeed than would be the case with Russia.
The problem now is choosing between shared values, military commitments, and common economic systems on one hand, which would favor Estonia and Bulgaria, or the much larger and lucrative Russian market, the stability of which could hinge on a serious deterioration in relations between West and East such as characterized the Cold War. Taking all into account, the wiser decision would be to foster improved relationships with Estonia and Bulgaria for the reasons given but to continue to do business with Russia with the understanding that the Russian government is entirely capable of seizing foreign assets on a moment's notice and prosecuting foreign businesspeople, or Russians employed by foreign corporations, for "crimes" that would not be credible in a Western country. Personally, I'd choose Bulgaria and Estonia.
https://ec.europa.eu/neighbourhood-enlargement/policy/conditions-membership_en

https://www.csis.org/analysis/russian-organized-crime-and-corruption

https://www.transparency.org/news/feature/corruption_perceptions_index_2016