For example, Russian citizens who have moved to Canada for permanent residence, after a specified period, can obtain Canadian citizenship. In doing so, they do not need to renounce their Russian citizenship. The same applies to citizens of other countries.
Another matter is what the laws are of the country whose citizenship you held before obtaining Canadian citizenship. For example, a number of countries prohibit their citizens from holding citizenship of other countries. In particular, Ukraine is one such country. When obtaining Canadian citizenship, Ukrainian citizens must renounce their Ukrainian citizenship, otherwise they violate Ukrainian laws.
Whether you are violating the laws of the country of which you are a citizen by obtaining Canadian citizenship should be determined from the competent authorities of that country. As the editorial board of "Russian Toronto" notes, citizenship laws change regularly, and various by-laws are introduced even more often. Therefore, before obtaining Canadian citizenship, it is advisable to clarify in the country of which you are a citizen what provisions regarding dual citizenship are currently in effect there.
Being a citizen of any country, you are subject to both the rights and obligations of that country's citizens. Accordingly, you must simultaneously follow 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 follow the laws of the country in which they are currently located. If you are a citizen of both Canada and Russia, then when you are in Canada, you should primarily follow Canadian laws; when you are in Russia, you should follow Russian laws.
In particular, Russia will not recognize you as a Canadian citizen if you have Russian 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 conflict and you will have to decide which country's laws you should violate in order not to violate the other's.
It is especially important to understand that if you find yourself in a difficult situation in the country of which you are a citizen, then official representatives of the other country, of which you are also a citizen, will no longer be able to help you.
For example, if you are a citizen of both Canada and Russia, and during a trip to Russia 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 you – they will be reasonably told that you are a Russian citizen and everything that happens is an internal affair of Russia.
In a similar situation, a person who has only Canadian citizenship has the full right to the involvement of Canadian official bodies in their fate – they will arrange for a lawyer and monitor compliance with detention regulations.
As we can see, for all the attractive aspects of dual citizenship, it also has its downside. Therefore, in some cases it is wiser to renounce previous citizenship when accepting Canadian citizenship.