Canada, like a number of other countries, recognizes dual citizenship. This means that an emigrant can simultaneously be a citizen of Canada and a citizen of their former country. However, as noted by Russian Toronto, for people from the former Soviet Union there are certain nuances.
For example, the Soviet Union did not recognize dual citizenship. Therefore, all who acquired citizenship of another country (for example, Israel) automatically lost Soviet citizenship. After the collapse of the USSR, many countries that had previously been part of it as republics adopted laws allowing dual citizenship. In particular, Russia began to recognize the right of its citizens to have citizenship of another country. Subsequently, unfortunately, these states refused to recognize dual citizenship, including Russia. It no longer allows its citizens to obtain citizenship of another country, but it does recognize dual citizenship for those who obtained it before the introduction of the citizenship law of 2002. By the way, Canada began to recognize dual citizenship only in 1977.
Currently, citizens of Russia, Ukraine, and other CIS countries who have moved to Canada for permanent residence can obtain Canadian citizenship after a specified period. In doing so, they do not violate Canadian laws - it will not hinder them from obtaining Canadian citizenship. True, in this case the laws of Russia or Ukraine will be violated, since these countries do not allow the acquisition of a second citizenship. Nevertheless, it is practically possible to obtain Canadian citizenship without losing the existing one.
Being a citizen of a country, you have all the rights granted by that state, as well as obligations. Accordingly, you should simultaneously be guided by the laws of the countries of which you are a citizen. In international practice, it is accepted that a person with dual citizenship should primarily be guided by the laws of the country in which they are currently located. If you are a citizen of both Canada and Ukraine, then when you are on Canadian territory, you should first of all be guided by Canadian laws; and when on Ukrainian territory, by the laws of that country. In particular, Ukraine will not recognize you as a Canadian citizen if you have Ukrainian citizenship. However, this provision is far from unconditional, and a situation may arise where the need to comply with the laws of each country may cause a contradiction and you will have to decide whose laws to violate in order to fulfill others.
It is especially important to understand that if you find yourself in a difficult situation in the country of which you are a citizen, official representatives of another country will no longer be able to help. For example, if you are a citizen of Canada and Ukraine and during a trip to Ukraine you find yourself in a difficult situation (for example, arrested on suspicion of committing a crime), then representatives of the Canadian embassy are unlikely to be able to help - they will reasonably be told that you are a citizen of Ukraine and everything that happens concerns the internal affairs of the country. In a similar situation, a person with only Canadian citizenship has every right to the participation of Canadian official bodies in their fate - they will arrange for a lawyer and monitor compliance with the rules for the treatment of prisoners.
Therefore, before applying for Canadian citizenship, decide for yourself whether you need the citizenship of your country. And if you decide that Canadian citizenship is enough, you should first renounce the one you currently have.