In my case:

I gave them a tentative itinerary. I told them I plan to fly on this date from/to this location then visit these places and then fly back from this place to this place.

Regarding invitation letter: I rather wrote it as purpose of visit, I said I have a friend xyz at xyz place and xyz address in Canada, wanna go to visit him. Also, heard about Canada from my Canadian work colleagues so always wanted to visit xyz place so wanna utilize my vacation during xyz month by visiting these parts of Canada.