I am in the process of completing a TM8 application for re-entry permit into the kingdom, for a retirement visa. Halfway down the first page it asks year and date of birth and then directly afterwards the next 2 spots ask for changwat and country. Do these 2 spots want the one's birth city and country ?

It could be the state, provenience or whatever the equal is called where you were born.

Birth city and country as stated in your passport.

Yes

Changwat means province not city.

Changwat means province not city.

In my Canadian passport, my birth place is stated as city and country, there is no mention of province. If I put in the province (changwat) as the form indicates, will immigration reject it since it won't match the passport?

They will not reject it because you gave them what they asked for. They will not compare it to your passport.

The departure and return dates are not important either. You can put any date you want in those spaces.

I think I can corroborate that they don't check the changwat/country one has entered on the TM.8 against the passport. I have a copy of all my forms for the years 2009-2013, and I put Cholburi/Thailand or Prachuap Khiri Khan/Thailand in those spaces. Ooops. (I was born in the USA)