Long story short, after my undergraduate program, I worked at university X for 3 years. After the 3 years of employment, I left my position to pursue a master's degree. 2 years after that, I graduated with a master's degree and now I am applying for a job at the Canadian federal government. The federal government is asking me for a list of reference.
I can ask 2 people from my previous job at the university X to be my reference. One is the team lead (call her Y), and the other (call her Z) is one of my co-workers who held more senior position than me.
I feel that the person Z can provide the federal government with more useful reference about me, because it was the person Z who gave me a job training as well as direct supervision. However, Z is now retired and is no longer part of the team that I used to work for.
Person Y had been the team lead while I worked at university X, and she is still the team lead now. Y can give me a good reference, but Y and I did not interact much while I worked for the team.
Between person Y and person Z, whom should I ask for a reference to increase my likelihood for getting the job at the federal government?