This extract from a government webpage mentions a Supreme Court decision but doesn't cite it:
The principles, qualifications and factors emerging from these court judgments on the duty of loyalty, including a decision of the Supreme Court of Canada, can be summarized as follows:
As always, the particular facts of any case would be assessed against the principles of any SCOC ruling. I think a key point of discussion would be that he doesn't identify as a federal employee.
- The duty of loyalty owed by public servants to the Government of Canada encompasses a duty to refrain from public criticism of the Government of Canada.
- Failure to observe the duty of loyalty may justify disciplinary action, including dismissal.
- However, the duty of loyalty is not absolute, and public criticism may be justified in certain circumstances.
- In determining whether any particular public criticism is justified and therefore not subject to disciplinary action, the duty of loyalty must be balanced with other interests such as the public servant's freedom of expression.
Fraser v. Public Service Staff Relations Board,  2 S.C.R. 455
The way the whole thing started was magnificently dumb.
Duty of Loyalty - Canada.ca
This paper was developed to describe, in general terms, the current thinking on duty of loyalty in the federal public sector. Its purpose is help employees and managers understand the key concepts and provide some assessment criteria for specific cases.
Key lines from the eventual SCC decision, which I think sums this up well:
Supreme Court of Canada said:"A public servant is required to exercise a degree of restraint in his or her actions relating to criticism of government policy, in order to ensure that the public service is perceived as impartial and effective in fulfilling its duties. It is implicit throughout the Adjudicator's reasons that the degree of restraint which must be exercised is relative to the position and visibility of the civil servant" (p. 467)