No

Different country versions can not be installed on the same machine regardless of the year.

Why?  Intuit has not said why, but best guess is file names, I expect the same file name has a slightly different use one country to another

Resolution for 'Canadian 2018 issue: 'Is it possible to have both US and Canadian 2018 QuickBooks Desktop installed on the same computer?' available: Yes.

The Canadian 2018 issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the Canadian 2018 issue yourself by looking for a resolution described in the article. If it is a complex Canadian 2018 issue or you are unable to solve the issue, you may contact us by clicking here or by using other Canadian 2018 support options.

For more information about resolving issues related to Canadian 2018 in Quickbooks/QBO or to get support for the issue 'Is it possible to have both US and Canadian 2018 QuickBooks Desktop installed on the same computer?', click the link below: