The short answer is that I don't know.
Bilingualism bonuses seem to pose an issue. Again, you're saying that bilingualism is an asset, not an essential skill. If the position requires bilingualism, it must be better paid. In other words, the overall salary must be improved. The federal public service needs to attract the best people, the people with the best skills.
A few years ago, I did a study for the Quebec treasury board on retaining young people in the public service. The salary isn't the main factor for them. People are in the public service for the common good, and bilingualism—meaning serving the public in both languages and promoting the use of both languages—is part of the common good. It's wrong to think that salaries or bonuses will solve everything. Bonuses were a thing of the past.
I would lean more towards better pay. Federal public service jobs must be competitive. The public service competes with the private sector, but it has its advantages. Its jobs are highly sought after and they provide major benefits in terms of both working conditions and the work that people do. People aren't there to make a profit tomorrow morning so that the company's share price can rise. People do other things, and they like that. You can count on that. If bilingualism is required to obtain these positions, yes, it costs money. If the people who want to enter the public service—and young people do—know that a good job requires bilingualism, they'll learn the other language.