Network Error when pushing CiviCRM button
Your page edit screen shows (I think) a URL of the form 'http://domain.ca/civicrm/wp-admin...' whilst the 404 error is looking for 'http://domain.ca/wp-admin/admin.php'. This suggests to me that you're using WordPress Multisite with CiviCRM active on a site that is not the main site. This is not supported at present - CiviCRM is only functional on the main site of a multisite instance.

Edit: this URL schema could also be the result of installing CiviCRM in a sub-directory. This is also unsupported, though it's an issue that's being addressed.