To verify that the use of cloud computing complies with Government of Canada standards, regardless of the company hired, Elections Canada had to do a threat and risk assessment, with the assistance of the Communications Security Establishment, which is Canada's technical authority in the area of information security. Having witnessed the security measures adopted in each case, I can say that the necessary level of security has been met, particularly when it comes to management of lists of electors.
Once the information is in the cloud, I believe it is secure. However, the way the people who have to handle it work is another matter.