Can a security guard have a baton as a defensive tool?

Only if the company sanctions such and your trained on the proper use for you will be liable for any damage which occurs as all contact is investigated.

A baton isn't defensive in nature.

I have absolutely NO CLUE what type(s) of weapon various types of security guards can legally carry in Canada.

I am 100% certain not all companies allow everything the law allows and MOST only allow what they require.

I am even more certain that NO ONE that asks Yahoo Answers, instead of an actual security company shouldn't be a security guard.

I'm interested being a officer with you

you need to ask your employer. they have their rules.

legally speaking, there's no law against ANYONE carrying a baton as a defensive weapon.

Only if he is level-3 (in the states) and licensed with the proper training to use it. Anything listed as a weapon will bring liability if used without documented training.

It depends what country he is in. It might be seen as an offensive weapon. 

I use my tool as a baton, so why not?