Upvote:1
I would just put the amount of time you are actually planning on staying in Canada. The important thing is that you don't overstay the date stamped in your passport.
Anything else is not really the truth, and that can get you into trouble. Suppose they look at your stuff and you have things associated with going to the U.S.- your credibility could be in question. And your fears of being refused entry at the U.S. border- do you really want to open that can of worms?
You will have to meet the requirements for admissibility, in the opinion of the CBSA, in any case, of course.