What's the process of applying for a France-Canada dual citizenship?

You don't apply for dual citizenship as strictly speaking there is no such thing - there are just people who happen to be citizens of two countries because they fulfil the conditions in both and both countries permit that. What you are really asking is "how do I become a French citizen?" Your father may still be one as dual citizenship has been permitted since 1973.

For yourself, in general, as a child of a French citizen (I assume he was still a French citizen when you were born?) you are also a French citizen already. I suggest enquiring of the French Embassy as to how you would go about getting a certificate of citizenship or a French passport, and I would guess you will need, at minimum, your birth certificate showing your father's name, his French birth certificate, and his marriage certificate, to prove you are French.

You can't apply for dual citzienship, if you're entitled to citizenship in a particular country then you simply apply for a passport. Some countries may require you to official register with the Embassy but it's not always necessary.

What you need to do is check with the French Embassy if you meet the requirements for citizennship & if you do then you apply for a French passport, which you will need to enter France & be treated as a French citizen. You will also need a Canadian passport to enter & exit Canada.

Just because your father was born in France does not necessarily means he is a french citizen.

You did not say anything about his parents citizenship where are they from ?

And if you father wants now to become a french citizen then you have your answer, he is not a citizen. At any rate it would be too late to become one by now and being out of the country.

On what passport did you father entered Canada ? And what year was he born ?

Bow down before a maple leaf and surrender yourself to the french prime minister and youre practically a citizen.